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This only applies for p-values not corrected for multiple testing

Posted by barwil on 13 Oct 2009 at 12:10 GMT

Let us also suppose that the study has 60% power to find an association with an odds ratio of 1.3 at α = 0.05. Then it can be estimated that if a statistically significant association is found with the p-value barely crossing the 0.05 threshold, the post-study probability that this is true increases about 12-fold compared with the pre-study probability, but it is still only 12 × 10−4.

This calculation assumes that the p-value of 0.05 is not corrected for multiple hypothesis testing. I'm not an expert in association studies, but I think it is considered a bad practice to use non-corrected p-values. If any correction for multiple hypothesis testing was applied (e.g. Bonferroni or Benjamini-Hochberg) the resulting ppv would be altered by 5 orders of magnitude...

No competing interests declared.