The National Maternal and Infant Health Survey is a nationally representative, population-based sample survey of children born in the U.S. in 1988. It was conducted by the National Center for Health Statistics. Black children and low birth weight infants were oversampled.

The same children were studied again in 1991, when their mothers were sent a second questionnaire asking about sociodemographic factors and child health.

At follow-up, mothers were asked for the names and addresses of all medical providers their children had seen for care since birth, as well as permission to contact those providers to release the children’s medical records. More than 90% of mothers consented.

Of these medical providers, 77% responded to the survey, providing information on more than 99 thousand inpatient, outpatient and emergency room visits by 6,201 children in the sample.