Re: teaching statistical methods by rules?
With all this discussion about methods and rules I thought that this question might be appropriate: Has anyone tried using "Comprehending Behavioral Statistics" by Russell T. Hurlburt, Brooks Cole, 1994 (that I saw) It seems to be the usual sort of intro stat text, but with a twist. He makes a large point of showing students how to "eyeball" a dataset and by doing this to be able to extract the parameters with a fairly high degree of accuracy. For each parameter he describes a technique to use, or sometimes a couple of alternate techniques to use. His claim is that the typical method that authors have been using results in students grinding away with calculators for tens of minutes and when they get a resulting number they often have no idea whether it is right or have any feel for what that number really represents. He does include all the usual formulas, he hasn't abandoned them. But he claims that the "eyeball" method can be done much more quickly and that allows him to have many many more such exercises done in class, allows students of differing skill levels to all work with some reward on such problems, etc. I was considering trying some of the ideas out and thought I would ask for opinions before subjecting students to one more questionable idea. Thanks ---== Posted via Newsfeeds.Com, Uncensored Usenet News ==-- http://www.newsfeeds.com The Largest Usenet Servers in the World! --== Over 73,000 Newsgroups - Including Dedicated Binaries Servers ==-
Re: teaching statistical methods by rules?
Yep!! As you say: "Why are people so obsessed with T and Z? " Perhaps it would be even better (easier?) to focus on F since F(df1,df2) = t^2(df2) (Reminder: when using a t-table, the p-values usually involve ONE-TAIL and when using the F-table, the p-values involve TWO-TAILS ) Example: The critical-value of t for probability of p = .05 at t(18) = 1.734 The critical-value of F for probability of p = .10 at F(1,18) = (1.734)^2 = 3.01 :-) -- Joe * Joe Ward Health Careers High School * * 167 East Arrowhead Dr 4646 Hamilton Wolfe* * San Antonio, TX 78228-2402San Antonio, TX 78229 * * Phone: 210-433-6575 Phone: 210-617-5400* * Fax: 210-433-2828 Fax: 210-617-5423 * * [EMAIL PROTECTED]* * http://www.ijoa.org/joeward/wardindex.html * - Original Message - From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Sunday, December 19, 1999 4:44 PM Subject: Re: teaching statistical methods by rules? | In article [EMAIL PROTECTED], | [EMAIL PROTECTED] says... | | snip | | On the other hand, a body of knowledge can be thought of as a set of | 'rules'. The important thing is that this set is constructed by the | individual, so our aim should not be to teach statistics as a set of | rules, but in such a way that each student can develop his or her own | set of rules. They won't be the same for all, and they will different | from the teacher's, but they hopefully will work. (If you like, this is | a defintion of a 'good student' - one who manages to construct a | successful set of rules for each subject. | | | It's either undergraduate students in Australia are much smarter than those | living in the United States or you live on a different planet. The last time I | taught an undergraduate introductory statistics class, some students couldn't | even do fractions and simple algebra. Can you expect them to develop their own | rules? | | Why are people so obsessed with T and Z? When the degrees of freedom exceeds | say 30, the difference between T and Z is practically negligible. You can use T | or Z in such a case. However, the P-value from Z is easier to compute. | | -- | Tjen-Sien Lim | [EMAIL PROTECTED] | www.Recursive-Partitioning.com | | Get your free Web-based email! http://recursive-partitioning.zzn.com | |
Re: teaching statistical methods by rules?
[EMAIL PROTECTED] wrote: In article [EMAIL PROTECTED], [EMAIL PROTECTED] says... snip On the other hand, a body of knowledge can be thought of as a set of 'rules'. The important thing is that this set is constructed by the individual, so our aim should not be to teach statistics as a set of rules, but in such a way that each student can develop his or her own set of rules. They won't be the same for all, and they will different from the teacher's, but they hopefully will work. (If you like, this is a defintion of a 'good student' - one who manages to construct a successful set of rules for each subject. It's either undergraduate students in Australia are much smarter than those living in the United States or you live on a different planet. The last time I taught an undergraduate introductory statistics class, some students couldn't even do fractions and simple algebra. Can you expect them to develop their own rules? My comment above has nothing to do with students' 'smartness' or with their level of skill (two different things!) It is simply a way of describing what learning is. Why are people so obsessed with T and Z? When the degrees of freedom exceeds say 30, the difference between T and Z is practically negligible. You can use T or Z in such a case. However, the P-value from Z is easier to compute. Your interpretation of 'practically negligible' is different from mine, that's all. And with a computer, the p-value for t is exactly as easy to compute as the p-value for z. Regards, Alan -- Tjen-Sien Lim [EMAIL PROTECTED] www.Recursive-Partitioning.com Get your free Web-based email! http://recursive-partitioning.zzn.com -- Alan McLean ([EMAIL PROTECTED]) Acting Deputy Head, Department of Econometrics and Business Statistics Monash University, Caulfield Campus, Melbourne Tel: +61 03 9903 2102Fax: +61 03 9903 2007
Re: GLIM mistake?
Miguel Verdu wrote: Posted also to comp.soft-sys.stat.spss where the same question appeared (and nobody answered). Hello. This is an output of GLM from SPSS 9.0 where the dependent variable FLOR (log transformed) was analysed by crossing 2 levels of the FIXED factor SEX with 2 levels of the RANDOM factor POP. The F for POP has been obtained by dividing MS POP/MS (SEX*POP) (0.06349/0.199=0.319). I think this is wrong because the F could be obtained by dividing MS POP/MS error (0.06349/0.05737=1.10). Can anybody tell me if I am right or wrong? Dependent variable: LOGFLOR Source TypeIII SS df MS F Sig. - Intersección Hipótesis 694.987 1 694.987 10945.783 .006 Error 6.349E-021 6.349E-02a SEX Hipótesis .449 1 .449 2.256 .374 Error .199 1 .199b POP Hipótesis 6.349E-02 1 6.349E-02 .319.673 Error .199 1 .199b SEX * POP Hipótesis .1991 .199 3.467 .066 Error 4.360 76 5.737E-02c - aMS(POP) bMS(SEX * POP) cMS(Error) A colleague wrote to SPSS a month or two ago about this issue. Following is the response that he received from them. You can also look in Searle (1971) Linear Models (Sec. 9.7, pp. 400-404) for a discussion of this. Response from SPSS: There are two different sets of assumptions that are commonly made concerning the status of interaction effects in models with random components. They can be assumed to be fixed effects restricted to sum to 0 over the levels of the fixed effects within each level of the random effects, or they can be assumed to be random variables. The error term assignment you want comes from the first set of assumptions. The error terms in SPSS are based on the latter, which is the more commonly used set of assumptions for general handling of potentially unbalanced data (BMDP and SAS, for example, also do it this way). David Nichols Principal Support Statistician and Manager of Statistical Support SPSS Inc.
Re: teaching statistical methods by rules?
Tjen-Sien Lim asks:
Why are people so obsessed with T and Z? When the degrees of freedom
exceeds
say 30, the difference between T and Z is practically negligible. You can
use T
or Z in such a case. However, the P-value from Z is easier to compute.
With appropriate tables or software, the P-value from Z is *not* any
easier to compute.
I don't think most of us here are "obsessed with T and Z" but, rather,
concerned by others' obsession with it. I see it as a needless confusion
and a waste of time. Moreover, it has been observed that the meme tends to
mutate in the wild from harmless superstition ("I should use Z when n30")
to actual error ("Anybody who uses t with n30 is wrong.")
*Instructors* should consider this as a pedagogical matter; the question
should ideally never arise in the classroom. Unfortunately, many textbooks
and instructors in other courses sow the seeds of this silly little
anachronism, and it may be necessary to weed them out.
-Robert Dawson
Re: Factor analysis
Haider Al-Katem wrote:
I have conducted a factor analysis on some questionnaire items. The
dependent variables that I am measuring for example ('Intention To Buy',
'Attitude towards a product' and 'Trust in buying the product from a
merchant' ) seem to load significantly high on two factors which leaves me
with a NOT SIMPLE FACTOR STRUCTURE.
I am assuming that since 'Intention To Buy', 'Attitude towards a product'
and 'Trust in buying the product from a merchant' all seem to be some type
of an ATTITUDE , the significantly high factor loadings on the two factors
may be justifiable.
Simple structure is present when each item loads high on one factor and
low on all of the others. You have not said whether the two factors you
extracted can be named (if the first factor is ATTITUDE TOWARD PRODUCT
X, then what is the second factor?). Confirmatory factor analysis (CFA)
is a special case of SEM (specifically the measurement model part of
SEM). I would say that 50 cases is probably too low to warrant much
confidence in the results of an exploratory factor analysis or CFA.
Chuck
--
Chuck Cleland
Institute for the Study of Child Development
UMDNJ-Robert Wood Johnson Medical School
97 Paterson Street
New Brunswick, NJ 08903
phone: (732) 235-7699
fax: (732) 235-6189
http://www2.umdnj.edu/iscdweb/
--
Re: Prediction Model Question
Thanks for your replies, I have 5 minutes to reply to some of your comments because my wife and friends are waiting for me to get home so we can go to New Orleans. 1. I agree with Joe that the term "dummy" in dummy coding is a rather dumb term to use for indicator variables. The terms is widely used in political science, sociology, and business/econometrics (e.g., see Mendenhall and McClave's A second course in business statistics: regression analysis). I'll start using the term indicator coding if that's okay. 2. Okay, I'll check out some interactions (probably two way based on substantive concerns). We will have about 15 predictor variables; hence, I don't think we will include all possible interaction terms! BTW, the reason I used the term prediction rather than explanation is because my objective was primarily predictive (we are trying to predict prices of corporate training events)...this use is consistent with Pedhazur's use of the term prediction in his book on multiple regression. The title of his book is Multiple regression in the behavioral sciences: explanation and prediction. 3. In effects coding as I was using the term, consistent with Pedhazur, one group always gets -1 (like the group always getting 0 in dummy/indicator coding). 4. I will post an example where dummy/indicator and effects coding provide different results when I get back from my trip. Pedhazur specifically recommends not using dummy coding for this reason in the 2nd and 3rd editions of his text on multiple regression. I'll supply page numbers later.. Thanks again for your thoughts. Burke
Re: teaching statistical methods by rules?
Herman Rubin wrote:
Robert Frick [EMAIL PROTECTED] wrote:
Jerry Dallal wrote:
Robert Frick wrote:
I know it is hard to make statistics fun, but FOLLOWING
RULES IS NEVER
FUN. Not in math, not in games, nowhere.
In math and in games, following rules isn't just fun,
IT'S THE LAW. In fact, you can't have fun unless
you follow them. :-)
Well, technically, most real rules tell you what not to do -- they
usually don't tell you what to do, because that isn't fun.
This is well put. The rules describe what is allowed, but
not which of the allowed possibilities to perform.
I can't help but feel we're using the word "rules" in different ways.
Any time you learn a new game, the first thing you learn is the rules,
a mix of can and can't do. ("The batter shall take his position within
the lines of the batter's box". The batter shall not have his entire
foot touching the ground completely oytside the lines of the batter's
box...") One of the reasons I enjoy mathematics
so much is that it is rule based. You follow the rules, you get to
someplace new. These new locations reached by following the rules are
called "publications". :-) 'Couse, that's also what makes it
tautological!
Happy holidays to all!
Re: Standards for Skewness
Skewness is only well defined for univariate distributions. The Johnson SU distribution approximation for the skewness distribution converts a Pearson skewness measure to a normal distribution Z value. As with all large data sets, a small skewness will show up as indicationg that the departure from normality is significant. Bollen in his book in page 421 gives D'Agostino's formulas for the computation. I can give you a version in BASIC if you are interested. It is generally accepted that D'Agostino's approximation gives reasonably accurate results for samples with N8. In the multivariate world, skewness is not clear. You may have only one variable out of p-1 variables that is highly skew, and a multivariate test will show no significance. The effects are mediated by the covariance and averaging effects of the matrix of the data as a whole. The whole (as a single number) poorly represents individual variable skewness. Bollen's formula 9.78 is wrong. It does not correspond to Mardia's outstanding work on multivariate skewness measures. I am working on this issue now. DAH - Original Message - From: Ronald B. Livingston To: [EMAIL PROTECTED] Sent: Monday, December 20, 1999 11:25 AM Subject: Standards for "Skewness" Hello: Are there "standards" for describing the skew of a distribution? For example, 0 to 1 = mild; 1 - 2 = moderate, etc. I am aware of tests of significance for skew, but withlarge samples practically any skew is significant. Any references would be appreciated. Sincerely, Ron
Re: teaching statistical methods by rules?
On 20 Dec 1999, Don Taylor wrote in part: Has anyone tried using "Comprehending Behavioral Statistics" by Russell T. Hurlburt, Brooks Cole, 1994 (that I saw) It seems to be the usual sort of intro stat text, but with a twist. He makes a large point of showing students how to "eyeball" a dataset and by doing this to be able to extract the parameters with a fairly high degree of accuracy. Sounds refreshing. Might even convey, sort of subliminally, the notion that accuracy (or precision) is something one might be interested in... snip, description of Hurlburt's approach I was considering trying some of the ideas out and thought I would ask for opinions before subjecting students to one more questionable idea. There are hardly any ideas worth considering that aren't questionable. Won't hurt students to have "one more questionable idea" to work with. They get plenty as it is, and usually without much concern for their "questionability" on the part of their mentors. Occupational hazard. Live with it. -- Don. Donald F. Burrill [EMAIL PROTECTED] 348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED] MSC #29, Plymouth, NH 03264 603-535-2597 184 Nashua Road, Bedford, NH 03110 603-471-7128
adjusting marks
My wife wants to adjust marks for a course she is marking. Does someone have a formula or something for using a bell curve to move them up or down? I have done this sort of thing about 15 years ago, but I can't remember any of it! --
Re: adjusting marks
Dear Why, Ted: Sign your query, and provide a usable return address, and someone might consider an answer. It might even be a useful one. But anonymous questions don't deserve a response. On Tue, 21 Dec 1999, Generic [EMAIL PROTECTED] wrote: My wife wants to adjust marks for a course she is marking. Does someone have a formula or something for using a bell curve to move them up or down? What reason have you (or your wife) for supposing that "a bell curve" applies, or ought to apply, to her students? If she wants to adjust marks, she presumably has some idea of what kinds of adjustments she wants to make, and why. Let her have the courage of her convictions. I have done this sort of thing about 15 years ago, but I can't remember any of it! Donald F. Burrill [EMAIL PROTECTED] 348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED] MSC #29, Plymouth, NH 03264 603-535-2597 184 Nashua Road, Bedford, NH 03110 603-471-7128
