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#101
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Numbers to think about
On 1 Aug 2006 14:45:15 -0700, "
wrote: What is the probability that FL's positive result is false? I don't know. In order to compute this, you need to have at least a decent guess at A) the fraction of the tested population that's clean B) the fraction that's dirty (okay, just B=1-A) Well, you've just pointed out why these Bayesian formulas don't work in a situation where you don't know the incidence of whatever it is that your measuring in the population, which is the case in this situation. Intuitively, the incidence of X in the population shouldn't matter regarding the probability of a false positive being indeed false because this seems to be a function of the test and the sample, but who am I to disagree with the late Reverend Bayes. Like you, Bayes often leaves me scratching my head. It took me quite a while to get the Monty Hall Problem. There must be a way to calculate the probability of a positive being false given the information we have. Perhaps the answer will not be as accurate as it could be if we had information on the actual number of dopers in the entire group, but there has to be a way. My guess is that the best estimate given the information we have is 1%. In any case, the probability of a positive result being false is not the ratio of false verses real positives in the total population. I assume even a Bayesian would agree with that. |
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#102
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Numbers to think about
On Tue, 01 Aug 2006 23:23:42 GMT, Keith wrote:
On Mon, 31 Jul 2006 20:52:10 +0200, Montesquiou wrote: Personally, I hope that FL is exonerated, but my hopes do not change probability theory. Of course, as you know, I have the same.. but opposit hope Of course, as an American, I can understand how a Frenchman might be happy to see an American stripped of his TdF title. BTW, how did you like the World Cup Final? A fabulous event obviously, hope you can enjoy it someday too...doubt it. ****wit. First of all Keith, this remark was for Monty and, judging from his response, he took it in the spirit that it was intended. Second, there's no need to be rude. |
#103
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Numbers to think about
Jack Hollis wrote: On Mon, 31 Jul 2006 04:24:15 GMT, Ed wrote: IN each of these cases, the accuracy of the test is 99% but the chance that a positive test is valid is very different - due to the actual number of true positives, low in the first case and high in the second. Absolutely not. What your proposing would be true if the results of a specific test were dependent on the number of samples tested and the number of dirty verses clean urines in the sample. However, this is not the case. All of the tests are independent events and, as such, the chance of a clean sample testing positive is always 1%. Independent events? same source sample? (split) same lab? same procedure? these are not independent events. separate days, separate custody of sample, different lab - would sound much more "independent" to me. -bdbafh |
#104
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Numbers to think about
On 1 Aug 2006 14:45:15 -0700, "
wrote: I don't have a reliable source for any of these numbers. If you go back to the _original_ post in this thread, it posits that the UCI does 12000 tests, found 380 positives, and pulls out of thin air the supposition that the test is 99% accurate. I agree that most of this thread is based on dodgy suppositions, but the theoretical discussion has been interesting nonetheless. |
#106
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Numbers to think about
KV wrote: It seems to me that if they used two independent labs, splitting the samples at time of collection, this could eliminate a lot of doubt. ditto. When I did research we used 3 labs. And we always got differrent results for the same sample. I don't understand why the UCI, and especially the riders union, don't demand that the samples be tested by several labs. |
#107
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Numbers to think about
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#108
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Numbers to think about
Tom Kunich wrote:
If some OTHER lab doesn't do the testing I simply won't accept the results. You could consider having your world reprogrammed to include this directive. |
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