st: Use of collapse (sum) in Multiple Imputation

[Alberto Zezza <azezza@hotmail.com>]

Dear Stata Users,

I am using Stata 11 for Windows (PC).

I have a dataset with both individual and family level variables. Individuals are uniquely identified by a variable pid, households by a variable hhid.

I have missing data for some individuals in an individual level variable x which I would like to impute, before summing it up over individuals within a household to obtain a household level variable to use in further analysis.

Is there a way to do that and carry on the analysis within the mi environment in the household level file?

I am currently doing the following, using an individual level data file:

mi set wide
mi register imputed x
mi register regular y z 
mi impute regress x y z, add(20)
mi exeq: sort hhid; collapse (sum) x _*, by (hhid)

but the command stops with an error when performing the collapse for m=M (20 in mi case) saying 

variable _mi_id does not uniquely identify observations in the master data
r(459);

The variable _mi_id is not 'visible' in my list of variables so I presume this si something Stata generates in the background to manage mi data.

Thanks,

Alberto Zezza 		 	   		  
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