Dear Stata Forum,

I am using mixed estimating a cross-classified multilevel model with three levels, where I have approximately 100 000 observations divided into 12 cohorts cross-classified with 8 periods both nested in 9 countries. When I run the code:
Code:
mixed DV IV1 i.IV2 || _all: R.cohort || period: || country: , variance

------------------------------------------------------------
                |     No. of       Observations per Group
 Group Variable |     Groups    Minimum    Average    Maximum
----------------+--------------------------------------------
           _all |          1    114,788  114,788.0    114,788
       essround |          8     13,509   14,348.5     14,887
        country |         72      1,164    1,594.3      2,289
it seems Stata cross-classifies also the country and period variable (8 periods * 9 countries = 72 groups), instead of simply estimating country as a third level above the second (cohort-period cross-classified) level.
What would be the right way to write the syntax so that Stata would not cross-classify country with period?

Thank you very much in advance for your answers!