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I don't understand how did they get to the number 71% percent for 0.05 p-value? 0.05 p-value means that there is 5% probability that (for a t-test as example)

by yread 13y ago

I don't understand how did they get to the number 71% percent for 0.05 p-value? 0.05 p-value means that there is 5% probability that (for a t-test as example) a difference in averages of two sequences (the statistic) is by chance and not because of difference in means of their underlying normal distribution. I assume that the "toss-up" means that there is no difference in the means in reality (so the null hypothesis is true). Am I understanding it correctly? Shouldn't in this case the probability of getting p-value < 0.05 be in fact less than 5% and not 29%? How did they get the 29%?

a_bonobo 13y ago
By Bayesian interpretation, for which they cite this paper (PDF): http://swfsc.noaa.gov/uploadedFiles/Divisions/PRD/Programs/ETP_Cetacean_Assessment/Of_P_Values_and_Bayes__A_Modest_Proposal.6.pdf http://swfsc.noaa.gov/uploadedFiles/Divisions/PRD/Programs/E... I'm not 100% sure how it works, and I've never seen it applied in biology, but this is medicine.
runarberg 13y ago
No, you've got it wrong. A p-value of .05 means that given a true null-hypotheses, you have a 5% chance of getting this result anyway. That is, if there is no difference in the population mean, than you still have a 5% chance of finding a sample that contains this difference anyway. Do you see the difference. The p-value doesn't tell you anything about the population, it only gives you information about your sample -- a confusion that this article was pinpointing. So what the 29% is telling you is that, the chances of finding a statistically significant result (p = 0.05) given a population factor of µ = 0 are up to 29%. Whereas given a population factor of µ = 0 the chances of getting a significant result (p = 0.05) is 5%. EDIT: erased a wrong and confusing claim.
- deleted 13y ago
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- yread 13y ago
  Thanks, can you also explain why 29%? EDIT: also, what is population factor µ? The difference in means?

by yread 13y ago

a_bonobo 13y ago

By Bayesian interpretation, for which they cite this paper (PDF): http://swfsc.noaa.gov/uploadedFiles/Divisions/PRD/Programs/ETP_Cetacean_Assessment/Of_P_Values_and_Bayes__A_Modest_Proposal.6.pdf http://swfsc.noaa.gov/uploadedFiles/Divisions/PRD/Programs/E... I'm not 100% sure how it works, and I've never seen it applied in biology, but this is medicine.

runarberg 13y ago

No, you've got it wrong. A p-value of .05 means that given a true null-hypotheses, you have a 5% chance of getting this result anyway. That is, if there is no difference in the population mean, than you still have a 5% chance of finding a sample that contains this difference anyway. Do you see the difference. The p-value doesn't tell you anything about the population, it only gives you information about your sample -- a confusion that this article was pinpointing. So what the 29% is telling you is that, the chances of finding a statistically significant result (p = 0.05) given a population factor of µ = 0 are up to 29%. Whereas given a population factor of µ = 0 the chances of getting a significant result (p = 0.05) is 5%. EDIT: erased a wrong and confusing claim.

deleted 13y ago
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yread 13y ago
Thanks, can you also explain why 29%? EDIT: also, what is population factor µ? The difference in means?