Hi everybody,

I have an issue with Stata.

I am new on Stata.

I want to perform Mann-Withney between two groups (as follow), but Stata says "no observations". I tried to destring my variables but it says "already numeric; no replace".

If someone has an idea, I will really appreciate it.

Thanks

. tabstat newpH1 newpH2, stat(n mean sd q min max)

stats | newpH1 newpH2
---------+--------------------
N | 67 42
mean | 7.416313 7.426238
sd | .0523358 .0754838
p25 | 7.383 7.393
p50 | 7.416 7.4245
p75 | 7.451 7.466
min | 7.247 7.101
max | 7.519 7.555
------------------------------

.
end of do-file

. ranksum newpH1, by(newpH2)
no observations
r(2000);