The Puerto Rican Maternal and Infant Health Study (PRMIHS) is a cross-sectional study designed to provide information on the determinants of poor infant health among Puerto Ricans. The PRMIHS entailed collection of personal interview data from 2,763 mothers of Puerto Rican infants sampled from the 1994 and 1995 birth and infant death records of six U.S. vital statistics reporting areas (Connecticut, Florida, Massachusetts, New Jersey, New York City, Pennsylvania) and the Commonwealth of Puerto Rico. The included U.S. states are those with the greatest number of births to Puerto Rican women each year. In 1994 and 1995, 72.3% of all births to mainland Puerto Rican women occurred in the included states.
The primary funding agency was the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Funds were also provided by the Maternal and Child Health Bureau and the Centers for Disease Control. The data were collected by the Institute for Survey Research at Temple University under a subcontract from The Population Research Institute, The Pennsylvania State University. The principal investigators are Nancy S. Landale (The Pennsylvania State University), R.S. Oropesa (The Pennsylvania State University) and Ana Luisa Davila (University of Puerto Rico).
Infant mortality is one of the foremost public health problems in the United States today. Although the infant mortality rate has declined throughout this century, the rate of decline has slowed in recent years. Moreover, racial and ethnic minorities continue to have strikingly higher rates of infant mortality than non-Hispanic whites. A major determinant of infant mortality, especially neonatal mortality, is low birth weight. The high prevalence of low birth weight among disadvantaged groups and the lack of improvement in recent years suggest that there continue to exist barriers to healthy behaviors during pregnancy and to adequate prenatal care. Understanding such barriers and developing policies to remove them require further attention to linkages between the socioeconomic position of minority groups, their family patterns, and maternal behavior.
The U.S. minority groups with the highest rates of infant mortality are African Americans, American Indians, and Puerto Ricans. Moreover, Puerto Ricans have significantly higher rates of low birth weight and infant mortality than other Hispanic groups. Despite these poor outcomes, we know little about the determinants of poor infant health among Puerto Ricans.
One reason for this gap in knowledge has been the paucity of data with which to study Puerto Rican infant health. Apart from data sets compiled from vital records, such as the Natality Files and the Linked Birth-Infant Death Data Sets of the National Center for Health Statistics (NCHS), there have been no representative data sources on which to base studies. National health surveys appropriate for research on infant health have included too few Puerto Ricans to allow for the study of Puerto Ricans as a separate group. Vital-records-based data are very useful because they include information on the full population of births to Puerto Rican women, but vital records contain information on only a few social and economic variables. More detailed information is often available from clinic-based samples, but such samples are rarely representative of the larger population of concern.
Thus, the PRMIHS was designed to provide a rich source of data for studies of the factors related to infant health outcomes among Puerto Ricans.
The PRMIHS sample represents Puerto Rican women who had a live birth or infant death in the study area between July 1, 1994 and December 31, 1995. The PRMIHS drew stratified samples from live births and infant deaths that were registered in Connecticut, Florida, Massachusetts, New Jersey, New York City, Pennsylvania, and the Commonwealth of Puerto Rico. The live birth sample was stratified by vital statistics reporting area, month of the vital event, and infant birth weight (less than 2500 grams; 2500+ grams). The death sample included the full population of death cases in each vital statistics reporting area during the designated time frame.
In the United States, live births were eligible for inclusion in the birth sample if the Hispanic ethnicity of the mother was designated as Puerto Rican on the birth certificate. Infants who died before their first birthday were eligible for inclusion in the U.S. death sample if they were identified as Puerto Rican on the death certificate or if their mother was classified as Puerto Rican on the birth certificate. Information on ethnicity is not included on the birth and death certificates in Puerto Rico because an extremely high percentage of island residents are of Puerto Rican descent. To avoid inclusion of non-Puerto Rican infants in the study, the screener used to determine eligibility for participation included a question on whether the focal infant was of Puerto Rican descent. Mothers who answered that their infant was not of Puerto Rican descent were excluded from the study. This screening question was used in both Puerto Rico and the U.S. states.
The study design called for locating the mothers of the sampled infants from the address information provided on the vital records and requesting their participation in a Computer Assisted Personal Interview (CAPI). All study interviewers were bilingual, and the questionnaire was available in both Spanish and English.
Response rates for the birth and death samples, respectively, were 79% and 74%. Roughly two- thirds of the interviews (1,946) were with mothers of infants sampled from the computerized birth certificate files maintained by the states and Puerto Rico. The remaining 817 interviews were with mothers of infants drawn from death certificates for infant deaths.
The PRMIHS birth sample is a stratified sample. Thus, the data must be weighted to produce estimates that represent the population of live births to Puerto Rican women in the study area during the specified period of time. The final birth sample weight is the product of three weighting factors: (1) the inverse of the probability of selection, (2) a nonresponse adjustment, and (3) a poststratification adjustment. Low-birth-weight infants had especially high probabilities of selection because they were oversampled in the PRMIHS. Failure to weight the PRMIHS data will lead to biased population estimates because some births (e.g., low-birth-weight births) are overrepresented and others are underrepresented.
The full population of infant deaths was drawn for the death sample. The final death sample weight is therefore based on only one factor: a nonresponse adjustment.
The birth and death samples can be combined to conduct analyses of infant mortality. The user should be aware that a small group of infants drawn into the live birth sample died before their first birthday (n = 79). These cases should be included in analyses based solely on the birth sample; however, they should be considered death cases in analyses of infant mortality. They have valid values for both the birth and death sample weights. For analyses based on the birth sample, the 79 overlapping cases should be weighted by the birth sample weight. For analyses of infant mortality based on the combined birth and death samples, the 79 overlapping cases should be assigned the death sample weight.
The PRMIHS data set contains information from the birth and death certificates, as well as the personal interviews with the mothers. The birth certificate provides information on demographic characteristics of the infant's parents, the mother's pregnancy history, pregnancy and birth complications, and characteristics of the newborn. The death certificate includes information on demographic characteristics of the decedent and the underlying cause of death. Many of these data items from the birth and death certificates are included in the PRMIHS data set.
The PRMIHS questionnaire was intentionally modeled after the questionnaire used in the 1988 National Maternal and Infant Health Study so that data from the two studies could be directly compared. The survey collected information on the following topics:
Special questionnaire modules also were developed on topics that are of particular importance for understanding the Puerto Rican population, including: