# How to apply Wilcoxon test to small sample with NAs?

I have the following data which show some values before and after a drug. I want to test whether the drug increased the mean. I think I should use Wilcoxon test, but I don't know what to do with missing values (NAs). Do I need to remove NAs and corresponding before values?

before after
2.2    NA
8.2    5.2
9.5    NA
10.5   4
12.5   6
10.5   3
9.7   10
11.5   NA

• You might want to know why the values are missing since that could bias your conclusion. If there's nothing systematic about the missingness (people don't have after measurements because they died, say) then I think you can safely throw them out. – dsaxton Dec 7 '15 at 14:20

First, you should consider if Wilcoxon is here the best choice. Check How to choose between t-test or non-parametric test e.g. Wilcoxon in small samples thread for great answer by Glen_b where he compares pros and cons of different hypothesis tests for small samples. It appears that in very small samples $t$-test may be the most robust choice.