# What is the p-value for one-tailed Kolmogorov-Smirnov Test? [duplicate]

I am healthcare professional with minimal knowledge on statistics.

I am comparing 2 anti-hypertensives for their efficacy in lowering blood pressure, Drug A is the current standard treatment and Drug B is a new drug which was expected to be more effective in lowering blood pressure.

Therefore, my null hypothesis will be there is no difference between efficacy of Drug A and Drug B in lowering BP. Alternative hypothesis will be drug B is more effective than Drug A in lowering blood pressure.

I know I have to use Kolmogorov-Smirnov Test to test for normality before using t-test or Mann-Whitney to test for significance.

The question here is, from what i understand is that the p-value should be halved for t-test or Mann-Whitney as my hypothesis is one-tailed, but how about p-value for Kolmogorov-Smirnov? Do we keep with p<0.05 or halved it to p<0.025? (I think i supposed to run one-sample KS test using blood pressure to test for normality)

Thanks, if can please explain in layman terms as I do not have statistical background.

## marked as duplicate by Alexis, kjetil b halvorsen, Peter Flom♦Jan 6 at 10:50

Unless there is another version, the one-sample Kolmogorov–Smirnov test is about testing whether or not a sample is compatible with a certain distribution $$F$$ or with a family of distributions $$F_\theta$$ (the null). The alternative is that the distribution or family of distributions is not behind the sample. As such there is no side, no larger or smaller distribution.
• I have not a clue about the context and no competence in this area of application. My point is much simpler: testing $F=F_0$ vs $F\ne F_0$ is quite different from testing $F=F_0$ vs $F\le F_0$. – Xi'an Jan 6 at 8:10