Exploratory comparative tests on differences in the proportions of improvement between the rhIL-11-treated groups and the placebo group were done, using a two-sided Fisher's exact test.

All reported P -values are based on two-sided tests and compared to a significance level of 5%.

Calculating p-values Using the permutation method to simulate the null distribution (no change) we can obtain a p -value for a two-sided test, as detailed below.

Alternative names are one-sided and two-sided tests; the terminology "tail" is because the extremes of distributions are often small, as in the normal distribution or "bell curve", pictured above right.

Empirical R:S is compared to neutral R:S by means of a two-sided test of the binomial distribution.

All analyses were conducted using two-sided tests with alpha set to 0.05.

In the case of a meta-analysis using two-sided tests, it is possible to reject the meta-analysis null hypothesis even when the individual studies show strong effects in differing directions.

Finally, we note that in general, UMP tests do not exist for vector parameters or for two-sided tests (a test in which one hypothesis lies on both sides of the alternative).

We would have been equally surprised if we had seen 49,581 female births, i.e. , so a frequentist would usually perform a two-sided test, for which the p-value would be .

All reported P-values are based on two-sided tests and compared to a significant level of 5%.