st: Imputation of missing values/dealing with multiple imputations in Stata

["Andrea Baccarelli" <andreastata5@hotmail.com>]

I am working on a dataset where the exposure of interest was measured in the 
plasma of the study subjects. The detection limit is variable (it depends on 
the amount of plasma available for the assay)

Two points:
1. I was suggested to use an imputation method, which assigns a value for 
each missing measurement by selecting a value from the assumed distribution 
using maximum likelihood parameter estimates, related to the approach 
described by Helsel [Helsel DR. Less than obvious - statistical treatment of 
data below the detection limit.  Environ Sci Technol 1990; 
24(12):1766-1774.].
I have seen that Stata has different commands to deal with missing values. 
Does anybody know whether there is any command available to perform this 
kind of imputation?

2. I need to impute missing values not only one time, but to use multiple 
imputation to reflect the uncertainty of the estimates (kind of a 
"bootstrap" procedure).
How to perform the analysis (linear regression, or any other kind of 
analysis) on the multiple imputations? SAS 8.0 has a new procedure (PROC 
MIANALYZE, SAS 8.0) that does exactly this.
Does anybody know whether it is possible to do it also in Stata?

Thanks,
Andrea


Andrea Baccarelli, MD, MPH
Genetic Epidemiology Branch
National Cancer Institute /  NIH
6120 Executive Blvd. - EPS 7110
Bethesda, MD 20892-7236
Tel. (301)-496-5786
Fax (301)-402-4489
baccarea@mail.nih.gov

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