In one clinical trial comparing one experimental regimen A with control regimen B in order to test whether or not the regimen A is superior than regimen B. The p value for the hazard ratio of progression free survival is reported as 0.009 in the paper. Even though it's statistical significant, but since the median survival time for patients with control regimen is in fact longer than that with experimental regimen, 12 months versus 8 months. In another word, the control regimen has better treatment effect.
What will be the p value for testing experimental regimen versus control? Will it be different from 0.009 if it's one-sided test?
Hi Ben, Thank you for your reply, which is pretty detail and very helpful. However, when I read the WIKIPEDIA at http://en.wikipedia.org/wiki/One-_and_two-tailed_tests#Applications for One- and two-tailed tests, it is said under section APPLICATIONS, at second paragraph, 'For a given test statistic there is a single two-tailed test, and two one-tailed tests, one each for either direction. Given data of a given significance level in a two-tailed test for a test statistic, in the corresponding one-tailed tests for the same test statistic it will be considered either twice as significant (half the p-value), if the data is in the direction specified by the test, or not significant at all (p-value above 0.5), if the data is in the direction opposite that specified by the test.'. I cannot relate 'the p-value above 0.5' to your calculation of one-sided p-value. I am not exactly sure why it's p-value above 0.5. I am able to understand your calculation though.