I'm performing a diagnostic method comparison study in which I have 2 groups; one assessed using the experimental method, and one assessed using the standard method. These groups are matched, with 3 standard per experiment.
Continuos variables measured are not normally distributed, and data is matched, thus I'm opting for the Wilcoxon matched-pair signed-rank test to compare variables between the groups.
Now, in Stata every command for comparison of groups (ttest, ranksum...) allows the by(group) option, but not -signrank- !
For example: ranksum age, by(cohort)
if I want to compare the age distribution between the groups (defined by var cohort). But -ranksum- is for unmatched data!
Thus, my question is how to, similarly to ranksum, perform -signrank- with a by(groupvar) option? -signrank- doesn't allow this by default.
Is there a user-written command for this?
I've seen the -reshape- command being used, but I'm not used to that and I don't really know how to use it.