Understanding code of Mixed effects model using Stata

Question

From a researcher using Stata I got data and the following code:

. xtmelogit choicea network2 treatment2 treatment3 trustor2 if (trustor>0) & 
      (period>0) || subgrid: || subjectidtr: , var

• Is it correct that || does not indicate some OR operator, but indicates a random effect? How is the ":" related?
• Does the IF statement here simply mean that only the cases will be selected that have a score of higher than 0 on trustor and period above 0?
• What is var exactly?

I have to implement it in R, but for now I am not sure if what I understand from it, is actually correct.

Answer 1

First bullet: yes. The variable before the colon is the variable identifying the groups, the variables (possibly none) after the colon are the random effects.

Second bullet: yes

Third bullet: short for variance, shows the random effects in terms of variances and covariances instead of standard deviations and correlations.

You can read the helpfile here: http://www.stata.com/help.cgi?xtmelogit