In Matlab I did run a Wilkoxon rank sum test to compare two variables. The number of observation -for each variable- was very small (N=7; for this reason I did not run a t-test, as I could not reasonably assume normality of data). I don't know how to evaluate the result of Wilkoxon test: response is significant but I'm worried about the very small sample size (only 7 observation...did I run a meaningful test?). For this reason I computed the statistical power of the test which, as far as I know, is the correct way to evaluate the "goodness" of test response (Am I right?). I used the Matlab function sampsizepwr which wants as argument the type-of-test (for example z-test, t-test, Chi-square, etc...). I guess it is 'z' but I'm not sure (Matlab page on Wilcoxon seems to suggests that ranksum uses z-statistics).
Question 1: is it meaningful to compute the statistical power of Wilcoxon test, when I have very small samples size?
Question 2: is it correct to use z-statistics (as argument of function sampsizepwr) for computing power of Wilcoxon test?