Examples include baby booties, bibs, and baby care packages. The woman completes the self-administered questionnaire. This questionnaire is a modified version of that used in mail surveillance. Part II is mailed to the mother 60 days after she leaves the hospital. Most states oversample low weight births.
Many states stratify by mother's race or ethnicity as well.
Annual sample sizes range from 1,600 to 2,500, divided among three to six strata. Mothers' responses are linked to extracted birth certificate data items for analysis. The availability of this information for all births is the basis for drawing stratified samples and, ultimately, for generalizing results to the state's entire population of births. Its availability for all sampled women, whether they responded or not, is key to deriving nonresponse weights. For each respondent, the initial sampling weight is the reciprocal of the sampling fraction applied to the stratum.