Re: what type of distribution on this sampling
Not to disagree with Randy Poe completely, but I think we can say something, especially if we make _some_ assumptions (mainly, that this comes from an intro class). "@Home" wrote: > I am trying to solve a ? which basically gives the following facts: > > population of unknown number > popu std dev of 27 > pop mean of 78 > sample of size n=81 > 2000 random samples > > The ? is: > > what is the sample mean? It will be an average of your 81 measurements, which will be pretty close to the pop. mean of 78. > > what is the std error (std dev of sample means) It will _estimate_ the stdev of the pop stdev/sqrt(n) = (pretty close to) 27/sqrt(81) = 3. > what shape would the histogram be? Central Limit Theorem, Randy! Distribution of sample averages will _tend_ toward a Normal, regardless of underlying pop dist. for n=81, 'tend' will be pretty darn close. Since 81 is 3 stdevs from 0, I expect some degree of asymmetry in the original dist., but it won't be huge. The original dist., of course, could be almost anything, and still prodcue those two values of the mean and stdev. Without knowing anything about how the numbers were obtained, we can't say much. > The sample mean is obviously 78 and I calculate the std error of the sample > means to be 3. OK. these do _not_ require any assumption of Normality. > However I can't put the whole picture together. I suspect the distrib would > be normal given the 81 samples, but is 3 a low number for a std error. Could be 0.03, and it would still tend toward a Normal. Just pretty narrow spread. > Is it possible to translate it into a z score without any addtional data. Yes. This may require the assumption of Normal, but thanks to the CLT, you've pretty much got that. > Also I assume that the population itself could take any form skewed, normal > etc and you still end up w/the same std deviation. Yup. > In other words is the std deve of 27 and mean of 81 in any way predictive of > what a histogram of a distribution would look like? Only tells you the 'central tendency' and the 'dispersion tendency.' Does not say anything about the rest of the shape. > > > Finally what difference does it make how many random samples you take (ie. > 100 or 1000). the more repeat samples, the more smooth your eventual histogram may become - more 'bins.' What counts with the CLT is n = 81, or lots. > What statistic or parameter does this speak to? You tell me, OK? Jay BTW, I couldn't send an email to your address. Did I get it wrong? -- Jay Warner Principal Scientist Warner Consulting, Inc. North Green Bay Road Racine, WI 53404-1216 USA Ph: (262) 634-9100 FAX: (262) 681-1133 email: [EMAIL PROTECTED] web: http://www.a2q.com The A2Q Method (tm) -- What do you want to improve today? = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
normal populations result in normal sampling distributions of means ... if one considers all possible samples non normal populations never result in exactly normal sampling distributions regardless of sample sizes (though to the naked eye you might not be able to tell the difference) the central limit theorem states ... that as n increases ... regardless of the shape of the non normal population ... that the normal distribution is a more and more reasonable APPROXIMATION to the shape of the sampling distribution ... but, it does not say that if n is sufficiently large ... the sampling distribution WILL be normal there is NO magical n size where it is ok or it is not ok to treat the sampling distribution of the mean as being (close enough) normal ... though, if you look at simulations you will find that even with small ns ... from rather non normal distributions ... the shapes of the sampling distributions look mighty darn similar to the nd i took 5000 samples of n=25 ... not very big samples ... from a chi square distribution with 2 degrees of freedom ... found the means and then made a dotplot first you see what the chi square (population) distribution looks like ... then the sampling distribution of means . : ::. ::: :: ::.. ... . . . .. +-+-+-+-+-+---C1 0.0 3.5 7.0 10.5 14.0 17.5 MTB > dotp c26 Dotplot: C26 .. :. :::.. .:. .. .::.. :::. .. ..: . +-+-+-+-+-+---C26 0.60 1.20 1.80 2.40 3.00 3.60 At 12:18 AM 9/21/01 +, @Home wrote: >Stan, > >Thanks for the detailed explanation. I have one follwoup ?. You say, > >"If the original population is normally distributed, the sample means >will also be normally distributed. Even if the original population >is skewed, the sample means will still be approximately normally >distributed given some assumptions, such as that the sample size >(81) is small compared to the population size (unknown). I don't >know enough to state all the conditions precisely." > >Asssume the facts already given. Suppose the population was some demographic >aspect of each person living in India, - n = 1 billion. The _mean_ of >sample means stays at 3. If the one billion population was badly skewed, is >it possible that a sample size of 81 would NOT result in a normal >distribution and would require a larger sample size. > > > >"Stan Brown" <[EMAIL PROTECTED]> wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > I'm just a journeyman in this area, but I'm going to presume to > > answer in hopes that if I make any errors the real gurus will > > correct me and the shame will facilitate my learning. :-) > > > > @Home <[EMAIL PROTECTED]> wrote in sci.stat.edu: > > >I am trying to solve a ? which basically gives the following facts: > > >population of unknown number > > >popu std dev of 27 > > >pop mean of 78 > > >sample of size n=81 > > >2000 random samples > > > > > >what is the sample mean? > > >what is the std error (std dev of sample means) > > >what shape would the histogram be? > > > > > >The sample mean is obviously 78 and I calculate the std error of the >sample > > >means to be 3. > > > > I think you mean the _mean_ of sample means? The mean of one sample > > could obviously be anything, though we expect it to be within 78-2*3 > > to 78+2*3 about 95% of the time. > > > > I calculate the standard error or the mean (sigma-sub-xbar) the same > > way you do, as sigma/sqrt(n) or 27/9 = 3. > > > > >However I can't put the whole picture together. I suspect the distrib >would > > >be normal given the 81 samples, but is 3 a low number for a std error. > > > > If the original population is normally distributed, the sample means > > will also be normally distributed. Even if the original population > > is skewed, the sample means will still be approximately normally > > distributed given some assumptions, such as that the sample size > > (81) is small compared to the population size (unknown). I don't > > know enough to state all the conditions precisely. > > > > >Is it possible to translate it into a z score without any addtional data. > > > > If the population mean and standard deviation are known, that's all > > you need for a z score. The formula is > > z = [ xbar - mu ] / [ SEM ] > > For your scenario, > > z = (xbar-78)/3 > > > > A sample mean of 60 has a z score of -6, so it is quite unlikely > > that you'd draw a s
Re: Free program to generate random samples
Rand really doesn't help. You need to put in separate arguments for the sample size n, number of repetitions, and location of the population array. "Jay Warner" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > In Excel, the random number generator is =RAND() > > Produces a number between 0 and 1, inclusive. Some peole dislikie its amount > of randomness, but for class purposes, it seems to work well. > > 2000 x 100 cells to get your sampel set is going to be big, but I think > do-able. > > Or, set up say 100 of the 100 sets. Then re-calculate 20 times. > > Jay > > "@Home" wrote: > > > Is there any downloadable freeware that can generate let's say 2000 random > > samples of size n=100 from a population of 100 numbers. > > > > Is this conceivable? for excel etc. > > > > = > > Instructions for joining and leaving this list and remarks about > > the problem of INAPPROPRIATE MESSAGES are available at > > http://jse.stat.ncsu.edu/ > > = > > -- > Jay Warner > Principal Scientist > Warner Consulting, Inc. > North Green Bay Road > Racine, WI 53404-1216 > USA > > Ph: (262) 634-9100 > FAX: (262) 681-1133 > email: [EMAIL PROTECTED] > web: http://www.a2q.com > > The A2Q Method (tm) -- What do you want to improve today? > > > > > > > = > Instructions for joining and leaving this list and remarks about > the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ > = = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
Stan, Thanks for the detailed explanation. I have one follwoup ?. You say, "If the original population is normally distributed, the sample means will also be normally distributed. Even if the original population is skewed, the sample means will still be approximately normally distributed given some assumptions, such as that the sample size (81) is small compared to the population size (unknown). I don't know enough to state all the conditions precisely." Asssume the facts already given. Suppose the population was some demographic aspect of each person living in India, - n = 1 billion. The _mean_ of sample means stays at 3. If the one billion population was badly skewed, is it possible that a sample size of 81 would NOT result in a normal distribution and would require a larger sample size. "Stan Brown" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > I'm just a journeyman in this area, but I'm going to presume to > answer in hopes that if I make any errors the real gurus will > correct me and the shame will facilitate my learning. :-) > > @Home <[EMAIL PROTECTED]> wrote in sci.stat.edu: > >I am trying to solve a ? which basically gives the following facts: > >population of unknown number > >popu std dev of 27 > >pop mean of 78 > >sample of size n=81 > >2000 random samples > > > >what is the sample mean? > >what is the std error (std dev of sample means) > >what shape would the histogram be? > > > >The sample mean is obviously 78 and I calculate the std error of the sample > >means to be 3. > > I think you mean the _mean_ of sample means? The mean of one sample > could obviously be anything, though we expect it to be within 78-2*3 > to 78+2*3 about 95% of the time. > > I calculate the standard error or the mean (sigma-sub-xbar) the same > way you do, as sigma/sqrt(n) or 27/9 = 3. > > >However I can't put the whole picture together. I suspect the distrib would > >be normal given the 81 samples, but is 3 a low number for a std error. > > If the original population is normally distributed, the sample means > will also be normally distributed. Even if the original population > is skewed, the sample means will still be approximately normally > distributed given some assumptions, such as that the sample size > (81) is small compared to the population size (unknown). I don't > know enough to state all the conditions precisely. > > >Is it possible to translate it into a z score without any addtional data. > > If the population mean and standard deviation are known, that's all > you need for a z score. The formula is > z = [ xbar - mu ] / [ SEM ] > For your scenario, > z = (xbar-78)/3 > > A sample mean of 60 has a z score of -6, so it is quite unlikely > that you'd draw a sample with a mean of 60. (My TI-83 says that the > area in the tail past z=-6 is just under 10^-9.) > > >In other words is the std deve of 27 and mean of 81 in any way predictive of > >what a histogram of a distribution would look like? > > I assume you meant to say "mean of 78 and sample size of 81"? > Assuming that, the histogram of sample means should be normal or > nearly so, with mean (mu-sub-xbar) 78 (same as population mean) and > standard deviation (standard error of the mean, sigma-sub-xbar) 3. > > >Finally what difference does it make how many random samples you take (ie. > >100 or 1000). What statistic or parameter does this speak to? > > None that I know, in a formal sense. If you take 100 random samples > of size 81, or 100,000 random samples of size 81, your histogram of > sample means will have the same shape, though the curve will be a > bit smoother with 100,000 samples. > > -- > Stan Brown, Oak Road Systems, Cortland County, New York, USA > http://oakroadsystems.com > My reply address is correct as is. The courtesy of providing a correct > reply address is more important to me than time spent deleting spam. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
At 06:28 PM 9/20/01 -0400, Stan Brown wrote: >None that I know, in a formal sense. If you take 100 random samples >of size 81, or 100,000 random samples of size 81, your histogram of >sample means will have the same shape, though the curve will be a >bit smoother with 100,000 samples. this is for sure ... here i generated 100 samples of n=25 from nd 50, 10 ... and then 10 samples of same size ... here are the dotplots and desc stats Dotplot: 100, 10 :: . . . : :. : ..:. :: :: : . . ...:.::.. . -+-+-+-+-+-+-100 Each dot represents up to 496 points . .:. . .::: .:. .: ... ... .:::.. -+-+-+-+-+-+-10 42.0 45.5 49.0 52.5 56.0 59.5 MTB > desc c27 c26 Descriptive Statistics: 100, 10 Variable N Mean Median TrMean StDevSE Mean 100100 50.224 50.036 50.190 1.941 0.194 10 10 50.006 50.017 50.007 2.003 0.006 Variable MinimumMaximum Q1 Q3 100 46.283 55.307 49.042 51.504 10 40.947 58.238 48.653 51.355 >-- >Stan Brown, Oak Road Systems, Cortland County, New York, USA > http://oakroadsystems.com >My reply address is correct as is. The courtesy of providing a correct >reply address is more important to me than time spent deleting spam. > > >= >Instructions for joining and leaving this list and remarks about >the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ >= == dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/drober~1.htm = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Bayesian estimation - variance function
I am estimating variance components for a model with heterogeneous error variances using Gibbs sampling. This is straightforward for a model where we simply classify records as to which error variance they represent, sampling from inverse chi-square distributions. Assuming error variances change with time, it would be preferable though to fit a variance function, e.g. a polynomial function of time, to model changes in error variance with time. Question is, how to do this ? what is the distribution of these polynomial coefficients to sample from (assuming data are multivariate normal). I would appreciate any pointers to publications dealing with this particular problem - to be honest, I am looking for a 'recipe' at this stage rather than in-depth theoretical treatment. cheers, karin. + Karin Meyer, Animal Genetics and Breeding Unit, University of New England, Armidale, NSW 2351, Australia, Phone (+61) (02) 6773-3331 Fax (+61) (02) 6773-3266 = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
WTC 9-11 stats show paranormal connection
>Subject: WTC 9-11 stats show paranormal connection (Report from Princeton U) > >http://noosphere.princeton.edu/ >please read and comment I'm not surprised by the results. The "materialistic" viewpoint that most extant science still clings to is clearly wrongheaded as shown by quantum physics as well as anticipated by numerous eastern philosophies. The implications of the work remind me of F Scott Fitzgerald's: "A universe of ineffable gaudiness spun itself out in his brain while the clock ticked on the washstand and the moon soaked with wet light his tangled clothes upon the floor. Each night he added to the pattern of his fancies until drowsiness closed down upon some vivid scene with an oblivious embrace. For a while these reveries provided an outlet for his imagination; they were a satisfactory hint of the unreality of reality, a promise that the rock of the world was founded securely on a fairy's wing." (from, The Great Gatsby) Jeff Rasmussen http://www.symynet.com website & graphic design quantitative software spirit of tao te ching paperback & taoism = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
I'm just a journeyman in this area, but I'm going to presume to answer in hopes that if I make any errors the real gurus will correct me and the shame will facilitate my learning. :-) @Home <[EMAIL PROTECTED]> wrote in sci.stat.edu: >I am trying to solve a ? which basically gives the following facts: >population of unknown number >popu std dev of 27 >pop mean of 78 >sample of size n=81 >2000 random samples > >what is the sample mean? >what is the std error (std dev of sample means) >what shape would the histogram be? > >The sample mean is obviously 78 and I calculate the std error of the sample >means to be 3. I think you mean the _mean_ of sample means? The mean of one sample could obviously be anything, though we expect it to be within 78-2*3 to 78+2*3 about 95% of the time. I calculate the standard error or the mean (sigma-sub-xbar) the same way you do, as sigma/sqrt(n) or 27/9 = 3. >However I can't put the whole picture together. I suspect the distrib would >be normal given the 81 samples, but is 3 a low number for a std error. If the original population is normally distributed, the sample means will also be normally distributed. Even if the original population is skewed, the sample means will still be approximately normally distributed given some assumptions, such as that the sample size (81) is small compared to the population size (unknown). I don't know enough to state all the conditions precisely. >Is it possible to translate it into a z score without any addtional data. If the population mean and standard deviation are known, that's all you need for a z score. The formula is z = [ xbar - mu ] / [ SEM ] For your scenario, z = (xbar-78)/3 A sample mean of 60 has a z score of -6, so it is quite unlikely that you'd draw a sample with a mean of 60. (My TI-83 says that the area in the tail past z=-6 is just under 10^-9.) >In other words is the std deve of 27 and mean of 81 in any way predictive of >what a histogram of a distribution would look like? I assume you meant to say "mean of 78 and sample size of 81"? Assuming that, the histogram of sample means should be normal or nearly so, with mean (mu-sub-xbar) 78 (same as population mean) and standard deviation (standard error of the mean, sigma-sub-xbar) 3. >Finally what difference does it make how many random samples you take (ie. >100 or 1000). What statistic or parameter does this speak to? None that I know, in a formal sense. If you take 100 random samples of size 81, or 100,000 random samples of size 81, your histogram of sample means will have the same shape, though the curve will be a bit smoother with 100,000 samples. -- Stan Brown, Oak Road Systems, Cortland County, New York, USA http://oakroadsystems.com My reply address is correct as is. The courtesy of providing a correct reply address is more important to me than time spent deleting spam. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
"The sample mean is the average of your actual sample values. It isn't "obviously" 78 or anything else, though it might be close to 78. And how did you calculate the standard error?" I stand corrected on this point. Thanks. "Randy Poe" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > "@Home" wrote: > > > > I am trying to solve a ? which basically gives the following facts: > > > > population of unknown number > > popu std dev of 27 > > pop mean of 78 > > With what underlying distribution? > > > sample of size n=81 > > 2000 random samples > > > > The ? is: > > > > what is the sample mean? > > what is the std error (std dev of sample means) > > what shape would the histogram be? > > How can you possibly know this without having the actual > sample? It's a random variable, it depends on your > sample. > > > > > The sample mean is obviously 78 and I calculate the std error of the sample > > means to be 3. > > The sample mean is the average of your actual sample > values. It isn't "obviously" 78 or anything else, though > it might be close to 78. And how did you calculate the standard > error? > > > > > However I can't put the whole picture together. I suspect the distrib would > > be normal given the 81 samples, but is 3 a low number for a std error. > > Now I'm really lost. From the fact that there are 81 samples, > you conclude the distribution is normal? And all you > know about the samples is that there are 81 of them? > > > > > > Is it possible to translate it into a z score without any addtional data. > > It isn't possible to say anything at all without additional data. > > - Randy = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
[ stripping a couple of Newsgroups from the list ] On Thu, 20 Sep 2001 17:08:42 -0300, Gus Gassmann <[EMAIL PROTECTED]> wrote: > Randy Poe wrote: > > > "@Home" wrote: > > > > > > Is there any downloadable freeware that can generate let's say 2000 random > > > samples of size n=100 from a population of 100 numbers. > > > > > > > Um. > > > > A sample of 100 from a population of 100 is going to > > give you the entire population. > > Um^2. Only if you sample without replacement. > Probably: google for > . I know there are examples for SPSS and SAS. -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
why does everything have to be free??? but ... go here first ... http://members.aol.com/johnp71/javastat.html scroll down to random number generators ... one example is http://ebook.stat.ucla.edu/calculators/cdf/index.phtml regular stat software does these sorts of things easily ... in minitab for example ... let's say i wanted to generate a sample of n=100 from a chis dist. with 3 degrees of freedom 9/20/01 5:50:36 PM Welcome to Minitab, press F1 for help. MTB > rand 100 c1; SUBC> chis 3. MTB > dotp c1 Dotplot: C1 . : :.: ..: . .. : :::.:: .:: ::.. . :.::: .. : .. . .. . . +-+-+-+-+-+---C1 0.0 2.5 5.0 7.5 10.0 12.5 MTB > desc c1 Descriptive Statistics: C1 Variable N Mean Median TrMean StDevSE Mean C1 100 3.399 2.785 3.219 2.404 0.240 Variable MinimumMaximum Q1 Q3 C1 0.144 11.483 1.549 5.048 or, 100 samples of n=100 from the same chisquare distribution MTB > rand 100 c1-c100; SUBC> chis 3. MTB > rmean c1-c100 c101 MTB > dotp c101 Dotplot: C101 . :: :: . . : :.. . :.: ::: . . : .:.:::.::..: ... : . . . -+-+-+-+-+-+-C101 2.40 2.70 3.00 3.30 3.60 3.90 h ... looks like the sampling distribution of the mean ... when the population is shaped like a chisquare 3 distribution ... has that funny looking normal like shape MTB > desc c101 Descriptive Statistics: C101 Variable N Mean Median TrMean StDevSE Mean C101 100 2.9789 2.9525 2.9733 0.2393 0.0239 Variable MinimumMaximum Q1 Q3 C1012.3895 3.7689 2.8695 3.1187 MTB > At 06:09 PM 9/20/01 -0300, Voltolini wrote: >I am interested in the same programs and if possible, >one that can generate normal, binomial, etc distributions > >Thanks for any suggestions !!! > >_ >Prof. J. C. Voltolini >Grupo de Estudos em Ecologia de Mamiferos - ECOMAM >Universidade de Taubate - Depto. Biologia >Praca Marcellino Monteiro 63, Bom Conselho, >Taubate, SP - BRASIL. 12030-010 > >TEL: 0XX12-2254165 (lab.), 2254277 (depto.) >FAX: 0XX12-2322947 >E-Mail: [EMAIL PROTECTED] > >- Original Message - >From: @Home <[EMAIL PROTECTED]> >To: <[EMAIL PROTECTED]> >Sent: Thursday, September 20, 2001 2:50 PM >Subject: Free program to generate random samples > > > > Is there any downloadable freeware that can generate let's say 2000 random > > samples of size n=100 from a population of 100 numbers. > > > > Is this conceivable? for excel etc. > > > > > > > > > > = > > Instructions for joining and leaving this list and remarks about > > the problem of INAPPROPRIATE MESSAGES are available at > > http://jse.stat.ncsu.edu/ > > = > > > > > >= >Instructions for joining and leaving this list and remarks about >the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ >= == dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/drober~1.htm = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
"Is it possible to translate it into a z score without any addtional data." Followup If all you have to go on is a standard error for the sample of 3 and a mean of 75, does that give you any hint how bunched at the mean the population is? Suppose the std error of the sample was 25 or something? "Edward Dreyer" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > >At 05:48 PM 9/20/2001 +, you wrote: > >>I am trying to solve a ? which basically gives the following facts: > >> > >>population of unknown number > >>popu std dev of 27 > >>pop mean of 78 > >>sample of size n=81 > >>2000 random samples > >> > >>The ? is: > >> > >>what is the sample mean? > >>what is the std error (std dev of sample means) > >>what shape would the histogram be? > >> > >>The sample mean is obviously 78 and I calculate the std error of the sample > >>means to be 3. > >> > >>However I can't put the whole picture together. I suspect the distrib would > >>be normal given the 81 samples, but is 3 a low number for a std error. > > > >2000 samples of size 81 according to info you provided; and sample > >standard deviation should be > >smaller than population standard deviation according to central limit theorem. > > > > > >>Is it possible to translate it into a z score without any addtional data. > >> > >>Also I assume that the population itself could take any form skewed, normal > >>etc and you still end up w/the same std deviation. > > > >All possible > > > > > >>In other words is the std deve of 27 and mean of 81 in any way predictive of > >>what a histogram of a distribution would look like? > >> > >>Finally what difference does it make how many random samples you take (ie. > >>100 or 1000). What statistic or parameter does this speak to? > > > >The sampling distribution will always approximate a normal distribution > >regardless of the shape of the > >population distribution -- again, the central limit theorem. > > > >hope his helps... ECD > > > > > > > > > > > > > > > > > > > >>= > >>Instructions for joining and leaving this list and remarks about > >>the problem of INAPPROPRIATE MESSAGES are available at > >> http://jse.stat.ncsu.edu/ > >>= > > > >___ > >Edward C. Dreyer > > > >Political Science > >The University of Tulsa > > > > > > ___ > Edward C. Dreyer > > Political Science > The University of Tulsa > > > > > = > Instructions for joining and leaving this list and remarks about > the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ > = = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
what about if n is only 15 and the population distribution is heavily skewed? Isn't there a balancing here. Of course w/81 samples, it is hard to conceive anything but a normal distrib based on the CLT. "Edward Dreyer" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > >At 05:48 PM 9/20/2001 +, you wrote: > >>I am trying to solve a ? which basically gives the following facts: > >> > >>population of unknown number > >>popu std dev of 27 > >>pop mean of 78 > >>sample of size n=81 > >>2000 random samples > >> > >>The ? is: > >> > >>what is the sample mean? > >>what is the std error (std dev of sample means) > >>what shape would the histogram be? > >> > >>The sample mean is obviously 78 and I calculate the std error of the sample > >>means to be 3. > >> > >>However I can't put the whole picture together. I suspect the distrib would > >>be normal given the 81 samples, but is 3 a low number for a std error. > > > >2000 samples of size 81 according to info you provided; and sample > >standard deviation should be > >smaller than population standard deviation according to central limit theorem. > > > > > >>Is it possible to translate it into a z score without any addtional data. > >> > >>Also I assume that the population itself could take any form skewed, normal > >>etc and you still end up w/the same std deviation. > > > >All possible > > > > > >>In other words is the std deve of 27 and mean of 81 in any way predictive of > >>what a histogram of a distribution would look like? > >> > >>Finally what difference does it make how many random samples you take (ie. > >>100 or 1000). What statistic or parameter does this speak to? > > > >The sampling distribution will always approximate a normal distribution > >regardless of the shape of the > >population distribution -- again, the central limit theorem. > > > >hope his helps... ECD > > > > > > > > > > > > > > > > > > > >>= > >>Instructions for joining and leaving this list and remarks about > >>the problem of INAPPROPRIATE MESSAGES are available at > >> http://jse.stat.ncsu.edu/ > >>= > > > >___ > >Edward C. Dreyer > > > >Political Science > >The University of Tulsa > > > > > > ___ > Edward C. Dreyer > > Political Science > The University of Tulsa > > > > > = > Instructions for joining and leaving this list and remarks about > the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ > = = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
" A sample of 100 from a population of 100 is going to > > give you the entire population" Right my example was flawed, assume n=80 and you run the sampling 1000 times. The random generated list you are sampling has 200 number. "Gus Gassmann" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Randy Poe wrote: > > > "@Home" wrote: > > > > > > Is there any downloadable freeware that can generate let's say 2000 random > > > samples of size n=100 from a population of 100 numbers. > > > > > > > Um. > > > > A sample of 100 from a population of 100 is going to > > give you the entire population. > > Um^2. Only if you sample without replacement. > > --- > > gus gassmann ([EMAIL PROTECTED]) > > "When in doubt, travel." > > > Remove NOSPAM in the reply-to address > > = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
Hi On Thu, 20 Sep 2001, @Home wrote: > Is there any downloadable freeware that can generate let's say 2000 random > samples of size n=100 from a population of 100 numbers. > > Is this conceivable? for excel etc. Easily done with various statistical software (e.g., SPSS, SAS), if you have access to such programs. Here is a basic Basic algorithm that does the trick randomize timer !seed random number generator ns = 2000 !number of samples = 2000 ops = 100 !number of observations per sample = 100 for s = 1 to ns for o = 1 to ops score = int(rnd*100)+1 !generate score from 1 to 100 next o,s Should be possible to do something similar with excel or database software. Best wishes Jim James M. Clark (204) 786-9757 Department of Psychology(204) 774-4134 Fax University of Winnipeg 4L05D Winnipeg, Manitoba R3B 2E9 [EMAIL PROTECTED] CANADA http://www.uwinnipeg.ca/~clark = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
I am interested in the same programs and if possible, one that can generate normal, binomial, etc distributions Thanks for any suggestions !!! _ Prof. J. C. Voltolini Grupo de Estudos em Ecologia de Mamiferos - ECOMAM Universidade de Taubate - Depto. Biologia Praca Marcellino Monteiro 63, Bom Conselho, Taubate, SP - BRASIL. 12030-010 TEL: 0XX12-2254165 (lab.), 2254277 (depto.) FAX: 0XX12-2322947 E-Mail: [EMAIL PROTECTED] - Original Message - From: @Home <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, September 20, 2001 2:50 PM Subject: Free program to generate random samples > Is there any downloadable freeware that can generate let's say 2000 random > samples of size n=100 from a population of 100 numbers. > > Is this conceivable? for excel etc. > > > > > = > Instructions for joining and leaving this list and remarks about > the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ > = > = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
In Excel, the random number generator is =RAND() Produces a number between 0 and 1, inclusive. Some peole dislikie its amount of randomness, but for class purposes, it seems to work well. 2000 x 100 cells to get your sampel set is going to be big, but I think do-able. Or, set up say 100 of the 100 sets. Then re-calculate 20 times. Jay "@Home" wrote: > Is there any downloadable freeware that can generate let's say 2000 random > samples of size n=100 from a population of 100 numbers. > > Is this conceivable? for excel etc. > > = > Instructions for joining and leaving this list and remarks about > the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ > = -- Jay Warner Principal Scientist Warner Consulting, Inc. North Green Bay Road Racine, WI 53404-1216 USA Ph: (262) 634-9100 FAX: (262) 681-1133 email: [EMAIL PROTECTED] web: http://www.a2q.com The A2Q Method (tm) -- What do you want to improve today? = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
Randy Poe wrote: > "@Home" wrote: > > > > Is there any downloadable freeware that can generate let's say 2000 random > > samples of size n=100 from a population of 100 numbers. > > > > Um. > > A sample of 100 from a population of 100 is going to > give you the entire population. Um^2. Only if you sample without replacement. --- gus gassmann ([EMAIL PROTECTED]) "When in doubt, travel." Remove NOSPAM in the reply-to address = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: how to compare generated values with the specified distribution basis
On 20 Sep 2001 11:05:08 -0700, [EMAIL PROTECTED] (Jon Cryer) wrote: >(quoting Robert: "even when N=20, a uniform distribution can be treated as > normal for most purposes.") > > I assume you meant to say that for N=20, the sample mean based on a random > sample from a uniform distribution can be assumed to have a normal > distribution for most purposes. > > Right? I thought he was intending the stronger statement: a lot of uniforms can be treated as normal, especially for small N and for moderate effect size. Conover, et al., showed the equivalency between doing (a) the old rank-order tests (like the MWW), and (b) simple t-tests, etc., on the rank-transformations. Robert waffles by saying 'most' purposes, so I have to find it easy to agree. When might you *not* treat a uniform, N=20 as normal? - perhaps when the R^2 is too high (above .90)? -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: for students (biology et al.) that hate numbers
> You can have them count the colors of candies in bags of M&Ms. The M&M > web site has the expected proportions published so they can do a > ChiSquare test against those proportions. Does anybody really care about the proportions of different colors in bags of M&Ms? > Do a class of brainstorming to find out what kinds of things they are > interested in. Now, this is advice that is impossible to improve upon! Do this and the battle's won. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Prerequisite for stats (was Re: for number haters)
> the level of mathematics > often does not go much beyond cross-multiplying to solve for an > unknown, There's part of the problem in a nutshell. There's no such thing as "cross-multiply". It's..what?..a trick? It epitomizes the shortcut that hides the rigor behind what's really going on--two application of "When equals are multiplied by equals, the products are equal"--and guarantees that the rigor is neither appreciated nor mastered. Is it any wonder that students brought up under such a system have problems with logic, understanding, and the proper way to formulate and solve a problem? = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
"@Home" wrote: > > Is there any downloadable freeware that can generate let's say 2000 random > samples of size n=100 from a population of 100 numbers. > Um. A sample of 100 from a population of 100 is going to give you the entire population. - Randy = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Free program to generate random samples
At 12:27 PM 9/20/2001 -0700, you wrote: >This Message was undeliverable due to the following reason: > >Each of the following recipients was rejected by a remote mail server. >The reasons given by the server are included to help you determine why >each recipient was rejected. > > Recipient: <[EMAIL PROTECTED]> > Reason:[EMAIL PROTECTED] unknown > > >Please reply to [EMAIL PROTECTED] >if you feel this message to be in error. >Reporting-MTA: dns; femail22.home.com >Arrival-Date: Thu, 20 Sep 2001 12:27:35 -0700 >Received-From-MTA: dns; cx385303-b.utulsa.edu (24.179.17.101) > >Final-Recipient: RFC822; <[EMAIL PROTECTED]> >Action: failed >Status: 5.1.1 >Remote-MTA: dns; mx10.mindspring.com (207.69.200.38) >Diagnostic-Code: smtp; 550 [EMAIL PROTECTED] unknown >Received: from cx385303-b.utulsa.edu ([24.179.17.101]) > by femail22.sdc1.sfba.home.com > (InterMail vM.4.01.03.20 201-229-121-120-20010223) with ESMTP > id > <[EMAIL PROTECTED]> > for <[EMAIL PROTECTED]>; Thu, 20 Sep 2001 12:27:35 -0700 >At 05:50 PM 9/20/2001 +, you wrote: >>Is there any downloadable freeware that can generate let's say 2000 random >>samples of size n=100 from a population of 100 numbers. >> >>Is this conceivable? for excel etc. > > >Both Excel XP and Quattro Pro 10 have routines for generating random >numbers; I don't know about earlier versions. > >ECD > > > > > >>= >>Instructions for joining and leaving this list and remarks about >>the problem of INAPPROPRIATE MESSAGES are available at >> http://jse.stat.ncsu.edu/ >>= > >___ >Edward C. Dreyer > >Political Science >The University of Tulsa > > _ Dr. Edward C. Dreyer Department of Political Science The University of Tulsa = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
> >At 05:48 PM 9/20/2001 +, you wrote: >>I am trying to solve a ? which basically gives the following facts: >> >>population of unknown number >>popu std dev of 27 >>pop mean of 78 >>sample of size n=81 >>2000 random samples >> >>The ? is: >> >>what is the sample mean? >>what is the std error (std dev of sample means) >>what shape would the histogram be? >> >>The sample mean is obviously 78 and I calculate the std error of the sample >>means to be 3. >> >>However I can't put the whole picture together. I suspect the distrib would >>be normal given the 81 samples, but is 3 a low number for a std error. > >2000 samples of size 81 according to info you provided; and sample >standard deviation should be >smaller than population standard deviation according to central limit theorem. > > >>Is it possible to translate it into a z score without any addtional data. >> >>Also I assume that the population itself could take any form skewed, normal >>etc and you still end up w/the same std deviation. > >All possible > > >>In other words is the std deve of 27 and mean of 81 in any way predictive of >>what a histogram of a distribution would look like? >> >>Finally what difference does it make how many random samples you take (ie. >>100 or 1000). What statistic or parameter does this speak to? > >The sampling distribution will always approximate a normal distribution >regardless of the shape of the >population distribution -- again, the central limit theorem. > >hope his helps... ECD > > > > > > > > > >>= >>Instructions for joining and leaving this list and remarks about >>the problem of INAPPROPRIATE MESSAGES are available at >> http://jse.stat.ncsu.edu/ >>= > >___ >Edward C. Dreyer > >Political Science >The University of Tulsa > > ___ Edward C. Dreyer Political Science The University of Tulsa = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: what type of distribution on this sampling
"@Home" wrote: > > I am trying to solve a ? which basically gives the following facts: > > population of unknown number > popu std dev of 27 > pop mean of 78 With what underlying distribution? > sample of size n=81 > 2000 random samples > > The ? is: > > what is the sample mean? > what is the std error (std dev of sample means) > what shape would the histogram be? How can you possibly know this without having the actual sample? It's a random variable, it depends on your sample. > > The sample mean is obviously 78 and I calculate the std error of the sample > means to be 3. The sample mean is the average of your actual sample values. It isn't "obviously" 78 or anything else, though it might be close to 78. And how did you calculate the standard error? > > However I can't put the whole picture together. I suspect the distrib would > be normal given the 81 samples, but is 3 a low number for a std error. Now I'm really lost. From the fact that there are 81 samples, you conclude the distribution is normal? And all you know about the samples is that there are 81 of them? > > Is it possible to translate it into a z score without any addtional data. It isn't possible to say anything at all without additional data. - Randy = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: how to compare generated values with the specified distribution basis
On Thu, 20 Sep 2001 15:54:24 +0200, "JHWB" <[EMAIL PROTECTED]> wrote: > Hm, hope I didn't make that subject to complex, resulting in zero replies. > But hopefully you can answer this: > > I have a N(20,5) distribution and based on that I generated 25 values using > Minitab and the Calc>Random data>Normal function. The result yielded a mean > of 19,083 and a standard deviation of 6,0148. > > Now, how can I compare these results numerically and graphically? Compared numerically: generating parameters were mean=20, SD=5; for N=25, the observed sample has mean= 19, SD= 6, If you assume there is a known, fixed mean=20 and SD=5, then the SE for N=25 is 1; and the t-test is 1.0 A graphical comparison of 2+2 points is dull, and usually is a waste of space. Especially to illustrate "nothing interesting." There's more potential if you draw 10 or 100 samples. > I mean, in the back of my head I have an image of a graph with a straight > line (the basis for the values) and the plotted dots of the actual generated > data following the line. It is hard to describe a one-dimensional plot of 25 points, since there is hardly anything *there* that is interesting or useful. - I don't parse the description, above, on first try; I don't generate a description that sounds like that one when I do the task myself, even after several tries; so I don't know what you are describing. "Box-and-whisker" is a style that structures some information. Still, one plot is not as interesting as a dozen. -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Free program to generate random samples
Is there any downloadable freeware that can generate let's say 2000 random samples of size n=100 from a population of 100 numbers. Is this conceivable? for excel etc. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
what type of distribution on this sampling
I am trying to solve a ? which basically gives the following facts: population of unknown number popu std dev of 27 pop mean of 78 sample of size n=81 2000 random samples The ? is: what is the sample mean? what is the std error (std dev of sample means) what shape would the histogram be? The sample mean is obviously 78 and I calculate the std error of the sample means to be 3. However I can't put the whole picture together. I suspect the distrib would be normal given the 81 samples, but is 3 a low number for a std error. Is it possible to translate it into a z score without any addtional data. Also I assume that the population itself could take any form skewed, normal etc and you still end up w/the same std deviation. In other words is the std deve of 27 and mean of 81 in any way predictive of what a histogram of a distribution would look like? Finally what difference does it make how many random samples you take (ie. 100 or 1000). What statistic or parameter does this speak to? = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: how to compare generated values with the specifieddistributionbasis
Jon Cryer wrote: > > Robert: > > "even when N=20, a uniform distribution can be treated as > >normal for most purposes." > > I assume you meant to say that for N=20, the sample mean based on a random > sample from a uniform distribution can be assumed to have a normal > distribution > for most purposes. > > Right? Yes; I was writing in the context of standard inferential techniques. (t tests, etc) -Robert = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Prerequisite for stats (was Re: for number haters)
In article <[EMAIL PROTECTED]>, Bruce Weaver <[EMAIL PROTECTED]> wrote: >On 20 Sep 2001, Jay Warner wrote: >> true math phobes may not like the idea of putting the equation details & >> number crunching up to software. the thinking involved in Dennis' list above >> is much harder. Even BC (before computers), it was not that important for the user of statistics to be able to do the calculations. However, setting up the problem is what is important. >> But I'd like to see what happens if a class could let go of the numeracy >> issues, and look at what is happening - the logic of the questions. Wonder if >> 'learning theory' can address the possibility of that happening. I question the use of "logic" here. It is not totally incorrect, but it does not fit into the framework of any kind of logic course. What is involved is the ability to use precise symbolic language, which is sadly lacking, even in those who have had computational mathematics classes. The general use of variables belongs with beginning reading; it is an augmentation of language. >Jay's last paragraph reminded me of something I question just about every >time I teach an introductory stats class: Why the heck have we made >successful completion of a 1st year math course the prerequisite in so >many cases? Certainly for intro stats classes aimed at non-math majors >(e.g., psychology & social science students), the level of mathematics >often does not go much beyond cross-multiplying to solve for an unknown, >and maybe coming to grips with logarithms. Why do they have to SOLVE equations? What is needed is the ability to take a complex problem, and FORMULATE the problem in symbols. Also, they do not need to know HOW to add or multiply, but what it means. The same holds for logarithms; you will find that most students, even with much more than a year of college mathematics, do not understand logarithms as exponents, but just as something to manipulate formally, and to use for calculations. I think that many of the >number haters can be helped over those hurdles. I think a greater problem >for intro stats students is understanding the LOGIC--the logic of >hypothesis testing, for example. (Some readers of this group might call >it the illogic of hypothesis testing, of course.) So in my opinion, a >BETTER prerequisite, if we must have one, would be a course in symbolic >logic. Just my two cents. A course in symbolic logic at the sentential calculus level will not help. At the predicate calculus level it might, but few have had this, and this is again not what is needed. This can be taught in elementary school (it has been), but finding teachers who can learn it might be a problem. What is needed is first to be able to use variables as the linguistic entities they are; it has nothing to do with mathematics. Secondly, they need to understand what the operations mean, and be able to formulate arbitrarily complicated problems with no idea of how to solve them; I would make this the "mathematics" requirement for college entrance, and at this time, most college graduates cannot do this. Third, to do anything intelligent with statistics, they need to understand the probability CONCEPTS, not the computations or equations. They do not need to know the formula for a binomial distribution or a hypergeometric distribution; they need to know when these occur. One of the problems with students (and even PhD philosophers) is that they assume equally likely far too often; avoid this. How many people with statistical problems realize that there are probability assumptions involved? And if they do, are they aware of which are the important ones? Transformations to make things normal are common, but they are likely to destroy whatever reasonable relations hold, and it is usually the case that normality is of little importance. -- This address is for information only. I do not claim that these views are those of the Statistics Department or of Purdue University. Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399 [EMAIL PROTECTED] Phone: (765)494-6054 FAX: (765)494-0558 = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
WTC 9-11 stats show paranormal connection (Report from Princeton U)
http://noosphere.princeton.edu/ please read and comment = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: how to compare generated values with the specified distribution basis
Robert: "even when N=20, a uniform distribution can be treated as >normal for most purposes." I assume you meant to say that for N=20, the sample mean based on a random sample from a uniform distribution can be assumed to have a normal distribution for most purposes. Right? Jon Cryer At 01:16 PM 9/20/01 -0300, you wrote: > > >JHWB wrote: >> >> Hm, hope I didn't make that subject to complex, resulting in zero replies. >> But hopefully you can answer this: >> >>snip > > The gotcha is that while these may be roughly equivalent questions for >(say) N=20, for N small deviations from normality are important and the >test is poor at detecting them; for N large, deviations from normality >do not matter very much but the test is hypersensitive. > > For instance: even when N=20, a uniform distribution can be treated as >normal for most purposes. However, it will generally fail the >Ryan-Joiner test at a 5% level! > > -Robert Dawson > > >= >Instructions for joining and leaving this list and remarks about >the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ >= > ___ --- | \ Jon Cryer, Professor Emeritus ( ) Dept. of Statistics www.stat.uiowa.edu/~jcryer \\_University and Actuarial Science office 319-335-0819 \ * \of Iowa The University of Iowa home 319-351-4639 \/Hawkeyes Iowa City, IA 52242 FAX319-335-3017 |__ ) --- V "It ain't so much the things we don't know that get us into trouble. It's the things we do know that just ain't so." --Artemus Ward = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: how to compare generated values with the specified distributionbasis
JHWB wrote: > > Hm, hope I didn't make that subject to complex, resulting in zero replies. > But hopefully you can answer this: > > I have a N(20,5) distribution and based on that I generated 25 values using > Minitab and the Calc>Random data>Normal function. The result yielded a mean > of 19,083 and a standard deviation of 6,0148. > > Now, how can I compare these results numerically and graphically? > > I mean, in the back of my head I have an image of a graph with a straight > line (the basis for the values) and the plotted dots of the actual generated > data following the line. What you have in mind is a normal scores plot. This appears under Graph > Probability Plot as the default option. The hypothesis tests that come with this should be treated with great caution (though testing the output of a RNG supposed to yield normally distributed output *is* perhaps a valid use!) People have been known to do one of these tests to see whether they must use a nonparametric inference technique such as a sign or WMW test on a certain data set. However, the hypothesis test answers the question "are these data improbable under conditions of perfect normality?" and by extension "is there evidence against perfect normality?". What you want to ask is "are these data probably from a population that is normal enough for the method to work?" The gotcha is that while these may be roughly equivalent questions for (say) N=20, for N small deviations from normality are important and the test is poor at detecting them; for N large, deviations from normality do not matter very much but the test is hypersensitive. For instance: even when N=20, a uniform distribution can be treated as normal for most purposes. However, it will generally fail the Ryan-Joiner test at a 5% level! -Robert Dawson = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Definitions of Likert scale, Likert item, etc.
- about the citation; and some musing. On 19 Sep 2001 18:11:59 -0700, [EMAIL PROTECTED] (dennis roberts) wrote: > At 05:14 PM 9/19/01 -0400, Rich Ulrich wrote: > > >It has Likert's original observations on writing > >an attitude scale (1932, which I had not seen elsewhere). dmr > > likert's work appeared in the archives of psychology ... #141 i think ... > in 1932 ... it was his dissertation work ... under the direction i think of > gardner murphy One of the 3 references cited is Murphy. It says #140, 1932, Archives of Psychology. > > the intention of likert's work was NOT to validate in any way ... the 3 > scales he used in that dissertation ... but, to show that a simpler method > of attitude item scaling would be about as useful as the much harder to do > ... thurstonian scaling ... equal appearing intervals i think > > for sure, it is simpler > > however, we have to keep in mind that this was 70 years ago ... i hope we > have learned a few things since then ... but, sometimes i wonder > [snip, start of my cited 'race' example, and sig.] We have learned that social attitudes are not -- contrary to the regard of some social scientists in the 1930s -- they are not permanent, essential parts of the soul; which might be measurable to nice precision. Attitudes on race and attitudes on sex roles underwent a sea-change during WW II, and the recognition of variability undermined the notion that re-measuring would pin down some useful 'true scores' for those attitudes. By comparison - the people today who think that what we measure as IQ is inherent-and-fixed are making approximately the same mistake. The political surveys that predicted Truman would lose to Dewey (famous error in the 1948 Presidential race) were based on questions asked 6 weeks (I think it was) before the election. - that should have been wise enough, if attitudes were fixed. Moreover, in order to less-offend a person's privacy, the pollsters asked, "Who do you think will win?" instead of the modern, "Who would you vote for if the election were today?" I'm saying we have learned something about attitudes, and that improves the logical manipulations we do, and conclusions that we are willing to draw. But look at the discussions we have had about the scoring of performance for students (and their schools). As statisticians, we are pleased with neither the measurements nor the uses made of them. Our direct tools for item development and scoring now include methods that (a) definitely: are more computer-intensive and (b) hopefully: yield scales that are more precise and reliable. But scale developers and attitude surveyors still mess up. I guess I am concluding that what we have learned about scoring, since then, has had some notable successes. But it is hard to keep an eye on successes -- compared to the everyday failures. We still see botch-ups people make when composing their items, and, later, when using their results. -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Factor analysis - which package is best for Windows?
you may wish to consider NCSS (they have a web site) provides essentially the same output as SAS but is run from templates not SAS language. Less expensive, good documentation, excellant support. However does not provide an audit trail--a necessary feature for some governmental / legal groups. PeterOut wrote: > [EMAIL PROTECTED] (Magill, Brett) wrote in message >news:<[EMAIL PROTECTED]>... > > Also check out R, a GNU implementation of the S language, most prominently > > known through its use in S-Plus. R is a fully featured statisitical > > programming environment. In its MVA (Multivariate) package, it includes > > routines for factor analysis using maximum liklihood estimation with varimax > > and promax rotations. > > > > I have installed R1.3.0 on my Windows system and have noted that MVA > is an add-on. The FAQ tells how to obtain these add-ons but only for > UNIX. Is this add-on actually available for Windows? If so, how do I > obtain it? > > Thanks, > Peter = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
how to compare generated values with the specified distribution basis
Hm, hope I didn't make that subject to complex, resulting in zero replies. But hopefully you can answer this: I have a N(20,5) distribution and based on that I generated 25 values using Minitab and the Calc>Random data>Normal function. The result yielded a mean of 19,083 and a standard deviation of 6,0148. Now, how can I compare these results numerically and graphically? I mean, in the back of my head I have an image of a graph with a straight line (the basis for the values) and the plotted dots of the actual generated data following the line. JHWB = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Viruses in EdStat
"E. Jacquelin Dietz" wrote: > > The EdStat list is not moderated -- no human sees the messages before > they are automatically forwarded to the list. > > Jackie Dietz > > Jerry Dallal wrote: > > > > "E. Jacquelin Dietz" wrote: > > > > > We have investigated the possibility of removing attachments from > > > messages before they are distributed to the EdStat list. This appears > > > to be impossible using our current majordomo software. > > > > What about not transmitting any message with an attachment? Right, but there's software and there's software. Even unmoderated lists can use filters. I realize that stripping attachments is a major operation, but I wondered whether filtering the entire message might be simple and straightforward. Apparently it's not. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: for students (biology et al.) that hate numbers
>From an old post... Plain Peanut Red 20% 10% Orange 10% 10% Yellow 20% 20% Green 10% 10% Blue10% 30% Brown 30% 20% WBW __ William B. Ware, Professor and Chair Educational Psychology, CB# 3500 Measurement, and Evaluation University of North Carolina PHONE (919)-962-7848 Chapel Hill, NC 27599-3500 FAX: (919)-962-1533 http://www.unc.edu/~wbware/ EMAIL: [EMAIL PROTECTED] __ On Thu, 20 Sep 2001, Rob MacTurk wrote: > Would you happen to have the exact location for the expected proportions of > M&M colors? I went to the M&M site and couldn't seem to locate it. > > Rob MacTurk > > "Paul Bernhardt" <[EMAIL PROTECTED]> wrote in message > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > You can have them count the colors of candies in bags of M&Ms. The M&M > > web site has the expected proportions published so they can do a > > ChiSquare test against those proportions. > > = > > Instructions for joining and leaving this list and remarks about > > the problem of INAPPROPRIATE MESSAGES are available at > > http://jse.stat.ncsu.edu/ > > = > > > > > = > Instructions for joining and leaving this list and remarks about > the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ > = > = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: for students (biology et al.) that hate numbers
Would you happen to have the exact location for the expected proportions of M&M colors? I went to the M&M site and couldn't seem to locate it. Rob MacTurk "Paul Bernhardt" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > You can have them count the colors of candies in bags of M&Ms. The M&M > web site has the expected proportions published so they can do a > ChiSquare test against those proportions. = > Instructions for joining and leaving this list and remarks about > the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ > = = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
