Multiple groups

[Nanni bu]

Dear all,
I'd like to compare multiple groups, hovewer I'm not able to find the exact syntasis. In particular, I'd like to conditionate the animal with diet 1 in experiment 1 and animal 1 in experiment 1 with diet 2. It sound like the following:


ranksum area if animale==1|diet==1|exp==1 & if animale==1|diet==2|exp==2, by(exp)

can you help me in find the exact syntasis

regards

[Nanni bu]

or maybe


ranksum area if animale==1 in exp==1 in diet==1 & if animale==1 in diet==2 in
exp==2, by(exp)

[Nick Cox]

If your two groups are say

animals with diet 1 in experiment 1

animals with diet 2 in experiment 2

then you need to define groups

 
gen group = cond(diet==1 & experiment == 1, 1, cond(diet == 2 & experiment == 2, .)) 

* or do it this way 
gen group = . 
replace group = 1 if diet == 1 & experiment == 1 
replace group = 2 if diet == 2 & experiment == 2 

ranksum area, by(group)

If animale is a further categorical variable, then the syntax will change.

The rules have to be that ranksum must be presented with a group variable defining just two distinct (non-missing) values.

In general, you are going too fast. In order not to get into horrible messes, become clear that

* if and in are quite different constructs. You can't mush the syntaxes together.

* if is specified at most once in commands like these.

* You are getting ands and ors the wrong way round.

 
animale==1 | diet==1 | exp==1

should be (from the rest of your post)

 
animale==1 &  diet==1 & exp==1

[Nanni bu]

Dear Nick,
thank you for your suggestion. I'll try..

all the best
Giovanni