25 patients receive treatment, and they each get a difference score (After-Before). 18 of them get positive scores. I would like to test the null hypothesis that p=0.5.
I know that
1-pbinom(17,25,0.5) gives me the probability of 18 or more patients getting a positive score. My question is, to calculate the p-value, why do we have to do
That is, why do we multiply by 2 here?