Re: Pooled relative risks
JFC [EMAIL PROTECTED] wrote: I am concerned in the way of calculating pooled relative risks, since it is interesting in some *meta-analytical* applications. See eg Rothman Modern Epidemiology P 196 et seq. -- | David Duffy. ,-_|\ | email: [EMAIL PROTECTED] ph: INT+61+7+3362-0217 fax: -0101/ * | Epidemiology Unit, The Queensland Institute of Medical Research \_,-._/ | 300 Herston Rd, Brisbane, Queensland 4029, Australia v = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Marijuana
David C. Ullrich wrote: considerable benefit for neurogenic bladder problems, I did not know that, but I know that the topic is of considerable interest to people with various other conditions. Yes, recent work at the National Hospital of Neurology and Neurosurgery in London, UK has shown that two cannibinoids administered in a spray considerably reduce urinary frequency and the number of time PwMS have to get up to pee during the night (a big problem). The researcher I was talking to said that there are cannibinoid receptors in the bladder and the cortex but not in the micuration control areas of the brainstem nor in the spinal cord. As is the fact that the Supreme Court seems to have decided that pi = 3 again... More like -6. Here I get a little lost again. Exactly what does it mean to say the relative risk is 4.8? I assumed it meant event A happened 4.8 times as much as would be expected if the two events were unrelated. And here again I'm _totally_ lost. Okay, put it like this: Of 1086240 trials, A happened in 17484 of them, B happened in 124 and both A and B happened in 9. I really need to know how to how to calculate the statistical implications here. Please someone help me! What I want to know is what is the correlation between these two event? Most importantly, how statistically significant is the result? Can any reasonable conclusions be drawn from these data - esp, in view of the small dataset size? Take care, Paul All About MS - the latest MS News and Views http://www.mult-sclerosis.org/ = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Marijuana
David Petry wrote: Keep in mind that correlation is not the same as causation. That's of particular importance in a study like this one. That is, if people are taking marijuana to treat pain and general discomfort, and if heart attacks are preceded by pain and discomfort, then there will be a strong correlation between marijuana use and later heart attacks, but it won't be proof of causation. I know the study is flawed in ever so many ways. I just want to get at the statistical implications. I wish I hadn't memtioned marijuana or the trial. Please help me to find the appropriate statistical test (e.g. two-tailed t-test, Spearman Rank correlation, chi2 test or whatever) and help me work out the statistical significance of any correlation between events A and B where: In 1086240 trials, A happened in 17484 of them, B happened in 124 and both A and B happened in 9. Is there a statistical association between A and B? How significant is that association? I would be ever so grateful if someone could help. Take care, Paul All About MS - the latest MS News and Views http://www.mult-sclerosis.org/ = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Marijuana
Paul Jones [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED]... snip So the research says that of a large number of people who had heart attacks at a centre, 124 people had used MJ in the year preceding the HA. Of these 9 reported that they had used MJ in the hour preceding the HA. All MJ users were questioned on the frequency with which they used MJ. The relative risk was reported as 4.8 - I used this to back-calculate that the average number of MJ usages per year rounded 141 - (9/n)/(115/(8760-n)) = 4.8 snip ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º° Surely this whole research is based upon a false premise. Isn't it like saying that 90%, say, of heroin users previously used soft drugs. Therefore, soft-drug use usually leads to hard-drug use - which does not logically follow. (A = B =/= B = A) Conclusions drawn from the set of people who have had heart attacks cannot be validly applied to the set of people who smoke dope. Rather than collect data from a large number of people who had heart attacks and look for a backward link, they should monitor a large number of people who smoke dope. But, of course this is much more expensive. Just my humble tupennyworth, Eamon ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º° = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
www.web-agri.com
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Re: Marijuana
In his redoubtable Re: Marijuana dated: 6/14/2001 5:47:23 PM Central Daylight Time, Jim Ferry wrote I was surprised to see this subject heading on sci.math. I thought it might have to do with the following lyrics (I forget the name of the group and the song): "I smoke two joints at two o' clock; I smoke two joints at four. I smoke two joints before I smoke two joints, And then I smoke two more." Given an infinite supply of marijuana, even granting immortality to Cheech and Chong would not make the above feat possible. One would need to have existed for an infinite amout of time. And even then, smoking a joint takes at least one Planck time unit, so if you plot on a time-line the points at which each joint-pair- smoking finishes, there can't be any accumulation points. This would seem to preclude any such feat of pot-smoking . . . unless you somehow exist in a strange temporal topology (e.g., the long line). So then, how much marijuana would one have to smoke to actually change the nature of (one's personal) time in such a way? I'm guessing that no finite amount would suffice, but do not hazard a guess as to the precise cardnality required. I read the above message by starting with the first word [I] and ending with the last word [required]. Therefore I read the whole thing along some sort of time line (to use Jim's term) Now hear this (I don't mean that literally of course).: I am utterly incapable of understanding the logic adduced in the last three paragraphs that come after the first paragraph as well as after the lyric which comes after the first paragraph and before the last three paragraphs. So now my question to Jim becomes: is what I'm about to say possible according his line of thinking [pun intended] ? I perused one paragraph at the beginning, I perused three paragraphs at the end. I perused one paragraph before I perused three paragraphs And then I perused three paragraphs more. To my untutored mind 'tis entirely possible because the third and fourth lines merely iterate the first and second. See the following exegesis : I perused one paragraph [that at the beginning] before I perused three paragraphs [those at the end] and then [having perused the paragraph at the beginning before going on to peruse the three paragraphs at the end] I perused three paragraphs more [i.e. the last three paragraphs] Now if you tell me that the aforegoing is impossible then --- whoopee --- I have done the impossible; because that is precisely what I did. Of course, you may retort: "Well hows come ya didunt say ya whatcha meant from da git go?" To which I could only sigh and reply: "Because I was engaging in a bit of whimsical wordplay, good sir --- and am inconsolably, irremediably, not to mention insincerely, sorry that you failed to comprehend what I was up to." Now think about this Jim, think real hard!!! Which seems more plausible, that that the unknown author(s) of the lyric you cite were 1) just having some fun with words, or 2) that they were deliberately constructing a verbal paradox in the sense of a self-contradictory statement that at first seems true but could be mathematically demonstrated to be false? Oh yes!!! If you opt for the second option, please support your decision mathematically. (I won't understand it of course. But what difference does *that* make? I will nevertheless be tremenjusly impressed) Su servidor [Sp: your servant --- but don't take that literally] Harley Upchurch, M.D. (No no!!! Not medical doctor, mathematical dummy.) .
Re: Marijuana
On Fri, 15 Jun 2001 08:02:23 +0100, Paul Jones [EMAIL PROTECTED] wrote: David C. Ullrich wrote: considerable benefit for neurogenic bladder problems, I did not know that, but I know that the topic is of considerable interest to people with various other conditions. Yes, recent work at the National Hospital of Neurology and Neurosurgery in London, UK has shown that two cannibinoids administered in a spray considerably reduce urinary frequency and the number of time PwMS have to get up to pee during the night (a big problem). The researcher I was talking to said that there are cannibinoid receptors in the bladder and the cortex but not in the micuration control areas of the brainstem nor in the spinal cord. As is the fact that the Supreme Court seems to have decided that pi = 3 again... More like -6. Here I get a little lost again. Exactly what does it mean to say the relative risk is 4.8? I assumed it meant event A happened 4.8 times as much as would be expected if the two events were unrelated. And here again I'm _totally_ lost. Okay, put it like this: Of 1086240 trials, A happened in 17484 of them, B happened in 124 and both A and B happened in 9. But analyzing it this way simply makes no sense. Those trials you're talking about are _far_ from independent; each trial is associated with a particular person, and there will be a very strong correlation between various trials for the same person at different hours. I really need to know how to how to calculate the statistical implications here. Please someone help me! I know that the way you've been putting things makes no sense. I suspect, but I don't know for sure, that to get the sort of information you want you need more data than what you've told us - you also need data on how many people in the general population, without heart attacks, do and do not smoke evil weeds. What I want to know is what is the correlation between these two event? Most importantly, how statistically significant is the result? Can any reasonable conclusions be drawn from these data - esp, in view of the small dataset size? You keep asking this. The size of the dataset is not the reason we cannot draw the sort of inferences you're interested in. Take care, Paul All About MS - the latest MS News and Views http://www.mult-sclerosis.org/ David C. Ullrich * Sometimes you can have access violations all the time and the program still works. (Michael Caracena, comp.lang.pascal.delphi.misc 5/1/01) = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Marijuana
On Fri, 15 Jun 2001 08:02:23 +0100, Paul Jones [EMAIL PROTECTED] wrote: Of 1086240 trials, A happened in 17484 of them, B happened in 124 and both A and B happened in 9. I really need to know how to how to calculate the statistical implications here. Please someone help me! It is simple to solve this problem using a Monte Carlo simulation, that is, an approximate permutation test. I would gladly do that, but I need to know the frequency of pot smoking among those 124. That is, how many hours each one spend smoking pot in a year. From this information we can calculate how likely that there will be 9 or more coincidences of smoking pot and having a heart attack given statistical independence. Sturla Molden = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Marijuana
On Thu, 14 Jun 2001, Chas F Brown wrote: Jim Ferry wrote: [ ... ] it might have to do with the following lyrics (I forget the name of the group and the song): I smoke two joints at two o' clock; I smoke two joints at four. I smoke two joints before I smoke two joints, And then I smoke two more. Suprisingly, the name of this song is Smoke Two Joints (by Sublime, available on the Mallrats Sound Track Album). It is also a vague echo of one the Earl of Rochester's poems which begins, I rise at Eleven, I dine about Two, / I get drunk before Sev'n; and the next Thing I do... The rest is unpublishable in this dignified company. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Marijuana
In article [EMAIL PROTECTED], Axel Harvey [EMAIL PROTECTED] wrote: It is also a vague echo of one the Earl of Rochester's poems which begins, I rise at Eleven, I dine about Two, / I get drunk before Sev'n; and the next Thing I do... The rest is unpublishable in this dignified company. He designs a web site dedicated to his proof of FLT? Wade = 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
Hi there, would someone please explain in lay person's terms the difference betwn. principal components, commom factors, and maximum likelihood estimation procedures for factor analyses? Should I expect my factors obtained through maximum likelihood estimation tobe highly correlated? Why? When should I use a Maximum likelihood estimation procedure, and when should I not use it? Thanks. Rita [EMAIL PROTECTED] Unlike the other methods, maximum likelihood allows you to estimate the entire structural model *simultaneously* [i.e., the effects of every independent variable upon every dependent variable in your model]. Most other methods only permit you to estimate the model in pieces, i.e., as a series of regressions whereby you regress every dependent variable upon every independent variable that has an arrow directly pointing to it. Moreover, maximum likelihood actually provides a statistical test of significance, unlike many other methods which only provide generally accepted cut-off points but not an actual test of statistical significance. There are very few cases in which I would use anything except a maximum likelihood approach, which you can use in either LISREL or if you use SPSS you can add on the module AMOS which will do this as well. Tracey = 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
_Psychometric Theory_, by Jum Nunnally to name one. haytham siala wrote: Hi, I will appreciate if someone can help me with this question: if factors extracted from a factor analysis were found to be reliable (using an internal consistency test like a Cronbach alpha), can they be used to represent a measure of the latent construct? If yes, are there any references or books that justify this technique? -- Timothy Victor [EMAIL PROTECTED] Policy Research, Evaluation, and Measurement Graduate School of Education University of Pennsylvania = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
