Re: Marijuana
In article [EMAIL PROTECTED], [EMAIL PROTECTED] (Eamon) wrote: (c) Reduced motor co-ordination, e.g. when driving a car Numerous studies have shown that marijuana actually improves driving ability. It makes people more attentive and less aggressive. You could look it up. = 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, 22 Jun 2001 18:45:52 GMT, Steve Leibel [EMAIL PROTECTED] wrote: In article [EMAIL PROTECTED], [EMAIL PROTECTED] (Eamon) wrote: (c) Reduced motor co-ordination, e.g. when driving a car Numerous studies have shown that marijuana actually improves driving ability. It makes people more attentive and less aggressive. You could look it up. An intoxicant does *that*? I think I recall in the literature, that people getting stoned, on whatever, occasionally *think* that their reaction time or sense of humor or other performance is getting better. Improving your driving by getting mildly stoned (omitting the episodes of hallucinating) seems unlikely enough, to me, that *I* think the burden of proof is the stranger named Steve. -- 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: Normality in Factor Analysis
Calculation of eigenvalues and eigenvalues requires no assumption. However evaluation of the results IMHO implicitly assumes at least a unimodal distribution and reasonably homogeneous variance for the same reasons as ANOVA or regression. So think of th consequencesof calculating means and variances of a strongly bimodal distribution where no sample ocurrs near the mean and all samples are tens of standard devatiations from the mean. Hi, I have a question regarding factor analysis: Is normality an important precondition for using factor analysis? If no, are there any books that justify this. = 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], Rich Ulrich [EMAIL PROTECTED] wrote: On Fri, 22 Jun 2001 18:45:52 GMT, Steve Leibel [EMAIL PROTECTED] wrote: In article [EMAIL PROTECTED], [EMAIL PROTECTED] (Eamon) wrote: (c) Reduced motor co-ordination, e.g. when driving a car Numerous studies have shown that marijuana actually improves driving ability. It makes people more attentive and less aggressive. You could look it up. An intoxicant does *that*? I think I recall in the literature, that people getting stoned, on whatever, occasionally *think* that their reaction time or sense of humor or other performance is getting better. Improving your driving by getting mildly stoned (omitting the episodes of hallucinating) seems unlikely enough, to me, that *I* think the burden of proof is the stranger named Steve. Hallucinating? On pot? What are YOU smokin'? Pot doesn't cause hallucinations -- although a lot of anti-drug hysteria certainly does. A cursory web search turned up these links among many others to support my statement. Naturally this subject is controversial and there are lots of conflicting studies. The consensus is that at worst pot causes minor driving impairment similar to many prescription medications. At least one study showed that pot users had FEWER fatal crashes than non users! And stranger named Steve? I've been on this newsgroup since 1995. Not as famous as James Harris, maybe, but certainly no stranger. This is a small sample of what came up when I entered marijuana driving into Google. Read and learn. http://www.norml.org/canorml/myths/myth1.shtml http://www.reconsider.org/issues/marijuana/driving.htm http://www.cannabisnews.com/news/thread1016.shtml http://www.marijuana-hemp.com/cin/facts/drivehi.shtml When the data were analyzed, cannabis consumers actually showed a lower likelihood of being involved in a fatal crash than that of a drug-free control group, though the difference was not judged to be statistically significant. http://www.hoboes.com/pub/Prohibition/Drug%20Information/Marijuana/Drivin g/Driving http://www.taima.org/en/driving.htm It was of some interest that cannabis tended to show a negative effect on relative risk when other drug groups showed an increase. http://www.norml.org.nz/norml/Marijuana/Driving.htm#abc981014 Steve L = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
probability that Xi = X1...Xn
Can anybody give me a hint about this problem? Let the random variables X1,...,Xn be independent and let M be the index of the maximum among them (i.e. M=i implies Xi = X1,...,Xn). We want to find nice formulas that calculate the distribution of M from the distributions of X1...Xn, that we suppose belonging to the same class of distributions: for instance if we assume that all of X1...Xn are normally distributed, with parameters (m1,v1),...,(mn,vn), we would like to obtain a formula of the kind Pr[M=i] = Fi(m1,...,mn,v1,...,vn) for every i=1..n. The problem is that the integral that calculates Pr[M=i] is quite complicated, and I haven't figured out how to express its value as a simple function of the parameters. = 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, 21 Jun 2001 21:14:44 -0700, Chas F Brown [EMAIL PROTECTED] wrote: David C. Ullrich wrote: On Fri, 15 Jun 2001 15:23:03 +0100, Paul Jones [EMAIL PROTECTED] wrote: David C. Ullrich wrote: 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. Okay then, how should it be analysed? I've explained at least twice why I do not believe it is _possible_ to draw the sort of inference you want to draw from the data you've given us. You must be reading _some_ of those posts or you wouldn't keep replying. Well, although I've agreed with most of your complaints about trying to derive any information from the scanty data shown, there is *something* we can notice about the data set which has some relevance. Let's say we look at a sampling of 100 people who have both had heart attacks within the last year and have smoked an aspirin an average of once a week during that year. Now, without knowing what the average percentage of people who smoke aspirin each year, and the average percentage of people who have heart attacks each year without smoking aspirin, these numbers alone would be pretty useless. But if 95% of the people in the data set had their 1 heart attack inside of 1 minute after smoking an aspirin, you'd have some reason to further examine the hypothesis that, for some segment of the population, smoking an aspirin could trigger a heart attack. (Of course it could also be that impending heart attacks bring on the desire to smoke aspirin, or some other hypothesis that correlates the two phenomena). One the other hand, one would expect if there were no immediate correlation between smoking aspirin and heart attacks, the average time between smoking aspirin and heart attack would be more like 1/2 week. This would then indicate that it was not particularly worthwhile to investigate an immediate link between asprinin smoking and heart attacks. That seems to be the type of correlation that was reported here - some distribution of MJ smoking, and its *temporal* correlation with heart attacks. Now, that says exactly nothing about whether MJ use increases or decreases the liklihood of having a heart attack in general (it could in fact in general *decrease* heart attacks, even in our data set); That's exactly right. When I say that there's nothing we can conlude from the data given I didn't mean there's _nothing_ we can conclude, rather nothing we can conclude _concerning_ the question of whether smoking increases the risk of a heart attack. I don't see how we can even quite conclude that the risk of a heart attack is higher among users immediately after smoking, for various reasons: I doubt that most users' use is uniformly distributed during the 24 hours of the day, I have no idea whether heart attacks are uniformly distributed throuought the day, so it could well be that the times people tend to smoke are the same as the times they tend to have heart attacks. Or they tend to smoke before meals (I knew some people like that years ago in college) and tend to have heart attacks after meals. Or they tend to smoke when they start to feel little chest pains, as someone suggested. Then even if it _is_ true that a smoker is more likely to have a heart attack immediately after smoking a joint, that does _NOT_ show that smoking increases the risk! Could be as you say that it actually decreases the risk, but regardless the time immediately after smoking is the riskiest time. So it seems clear to me that there is _nothing_ we can conclude about whether smoking increases the risk of a heart attack - it also seems clear that that is _the_ question of interest here. Not that I'm claiming that it _is_ the case that smoking decreases the risk of heart attack although the hour immediately afterwards is the riskiest time. I have no reason to think that's so. Also no reason to think it's not so: People who assume such a thing is ridiculous think so because they've classified the world into Good things and Bad things - actual things in the world are not that simple: (i) Aspirin is a Good thing. Good for pain and fever relief, and actually an aspirin a day helps prevent heart attack or stroke, I forget which. The reason I forget which is it's irrelevant to me: For me aspirin is a Very Bad thing, because of other medical problems. (ii) Alcohol is a Bad thing. Except for that bit about how a glass of red wine a day is good for you, in terms os risk of heart attack or stroke, again I forget which. Alas, it doesn't follow that a quart of whiskey a day is good for you. Given that there _are_ plenty of legitimate medical uses for marijuana and given that the interaction between the body and chemicals is simply _not_ a matter of some chemicals Good and some Bad, the idea that
Re: calculation of an effect size with medians
Marc wrote: As a part of a report I have to perform a meta-analysis of some clinical trials. These trials report the median effect in the treatment group and the median effect in the control group (days of hospitalization). P-values from Mann-Whitney U-Tests are reported and the numbers of patients in treatment and control. My Question: How can I calculate an effect size (eg median difference between treatment and control)and confidence intervals with that data? You'd need raw data to calculate the effect size for Mann-Whitney test. Regards, Konrad = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
