Sampling design for the Birth in Brazil: National Survey into Labor and Birth.

This paper describes the sample design for the National Survey into Labor and Birth in Brazil. The hospitals with 500 or more live births in 2007 were stratified into: the five Brazilian regions; state capital or not; and type of governance. They were then selected with probability proportional to the number of live births in 2007. An inverse sampling method was used to select as many days (minimum of 7) as necessary to reach 90 interviews in the hospital. Postnatal women were sampled with equal probability from the set of eligible women, who had entered the hospital in the sampled days. Initial sample weights were computed as the reciprocals of the sample inclusion probabilities and were calibrated to ensure that total estimates of the number of live births from the survey matched the known figures obtained from the Brazilian System of Information on Live Births. For the two telephone follow-up waves (6 and 12 months later), the postnatal woman's response probability was modelled using baseline covariate information in order to adjust the sample weights for nonresponse in each follow-up wave.