tag:blogger.com,1999:blog-9959776.post3770274605000342648..comments2024-02-15T04:42:41.606+00:00Comments on James' Empty Blog: On the importance of Bayesian analysisJames Annanhttp://www.blogger.com/profile/04318741813895533700noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-9959776.post-35462271736453342322007-09-15T01:04:00.000+01:002007-09-15T01:04:00.000+01:00Ah, yes I see now. Thanks for the clarification.Ah, yes I see now. Thanks for the clarification.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-72292269017352260442007-09-14T17:59:00.000+01:002007-09-14T17:59:00.000+01:00My point was not to criticize your analysis - it i...My point was not to criticize your analysis - it is indeed simple, but informative and correct. I was criticizing the characterization of this analysis as being Bayesian, and supposedly demonstrating "the importance of Bayesian analysis".<BR/><BR/>The analysis you made regarding the chance to get become mortally ill is a standard likelihood analysis, which would enable you to find a very significant p-value, and reject the null hypothesis (i.e., that the drug is not dangerous) in a rigorous frequentist framework.<BR/><BR/>Like any such likelihood analysis, you can then add prior information and make Bayesian statements about posterior probabilities.<BR/><BR/>Since the substantive argument can be made without the prior information (and is in fact more convincing that way, since it does not involve arbitrary prior models), this case does not serve as a demonstration of the importance of Bayesian analysis. It does demonstrate the importance of using appropriate likelihood models.Yoram Gathttps://www.blogger.com/profile/04291094497561607499noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-4759083937262053642007-09-14T07:48:00.000+01:002007-09-14T07:48:00.000+01:00Well, I never claimed I had done more than a rathe...Well, I never claimed I had done more than a rather trivial and naive exploration of the way the data could be analysed, but I'm not sure I understand your point. I did write:<BR/><BR/><I>Given an extremely complacent prior belief that the test is harmless with probability 0.999</I><BR/><BR/>which seems to me to be a pretty clear statement of (strong) prior belief that the drug is harmless.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-71885723341008488042007-09-14T07:11:00.000+01:002007-09-14T07:11:00.000+01:00Your analysis is not Bayesian. The extra informati...Your analysis is not Bayesian. The extra information about the probability of occurrence of a death-threatening situation under non-drug conditions is part of the likelihood model. It does not imply a prior distribution about the effect of the drug.Yoram Gathttps://www.blogger.com/profile/04291094497561607499noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-5781432014707149202007-09-05T22:08:00.000+01:002007-09-05T22:08:00.000+01:00No, if I had scoured the world looking for an ill ...No, if I had scoured the world looking for an ill person and then blamed the illness on some arbitrary factor (or their inherent evilness) I would have been making his error (at least, one of his errors). But there were only 6 people who took the drug in the first place.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-46979994048372523352007-09-05T21:16:00.000+01:002007-09-05T21:16:00.000+01:00But James,Aren't you misusing statistics in the sa...But James,<BR/><BR/>Aren't you misusing statistics in the same way as Professor Meadows? See:<BR/>http://www.timesonline.co.uk/tol/news/uk/article536728.eceAlastairhttps://www.blogger.com/profile/15152292130415788120noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-21651800234722946332007-08-29T08:25:00.000+01:002007-08-29T08:25:00.000+01:00Of course my example calc was rather trivial - I w...Of course my example calc was rather trivial - I was just trying to give a flavour of things. Eg, the fact that there is a clear link between the action of the drug and the nature of the illness is also highly relevant.James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-2819772141498779002007-08-28T12:44:00.000+01:002007-08-28T12:44:00.000+01:00Actually, the odds would seem to be 3.6% of the od...Actually, the odds would seem to be 3.6% <B>of the odds that a problem would hit exactly 6 of the subjects</B>. Which is even lower odds than I suggested above. But still well above 1/10^24.<BR/><BR/>Of course, if there's a gas leak or ebola infection, we'd expect the researchers to be subject to the risk as well, depending on how and when the facility is occupied (maybe it takes 24 hours for the gas to make one ill, and the researchers have 8-hour shifts).DWPittellihttps://www.blogger.com/profile/02809996471988559374noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-19071740047379329392007-08-28T12:33:00.000+01:002007-08-28T12:33:00.000+01:00If the odds of each person getting sick are 0.0001...If the odds of each person getting sick are 0.0001, or 1/10^4, then the odds of all 6 getting sick independently are 1/10^24 - reasonably defined as "impossible" in the real world.<BR/><BR/>The two controls reduce the possibility that the subjects were sickened by something else in their laboratory environment, such as a gas leak, or ebola.<BR/><BR/>The odds that the 6 would get sick and the 2 would not, given a problem in the laboratory environment, would seem to be 3.6%, as you write.<BR/><BR/>But until you quantify the odds of that sort of environmental problem you can't get a final answer of the total odds of this happening. The odds of such a laboratory problem would appear to be very small, but not nearly as small as 1/10^24.DWPittellihttps://www.blogger.com/profile/02809996471988559374noreply@blogger.com