I have talked with some people in the DHS office who are familiar with the Benin 2011-12 survey. They say that only a 1/3 subsample of women 15-49 were given the hemoglobin test. I see from the data file that there were 16,599 women and 5,513 had the test, which is almost exactly 1/3. Of the 5,513 women, 454 have code "9", which is not part of the label but would be the actual number "missing". The code ".", as I said before, means "not applicable". These numbers are unweighted.

I have looked very briefly at the report and the questionnaire. I cannot see anything about the subsampling or eligibility for this test. But maybe I am missing it because my French isn't good enough.

Apart from the subsampling, I have to warn you that DHS had problems with the implementing agency for this survey. Height and weight data were collected but are omitted from the report because of evidence of poor quality. That's very unusual. The anemia data should probably also have been suppressed. I think there should be some more explicit warnings, but I believe the report does describe, somewhere, the field problems and concerns about quality. Appendix C includes tables that indicate relatively high levels of genuinely missing responses (indicated by "9", "99", etc., rather than ".").

I believe that Benin is a special case. If you find other surveys with high levels of ".", I hope the report will provide documentation of subsampling. Let me know if you have other related questions.