Puerto Rican Maternal and Infant Health Study
Research Design and Methodology
Sample Design
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.
Sources of Information
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:
- infant mortality
- birth weight
- maternal health habits during pregnancy (e.g., nutrition, smoking, alcohol and drug use)
- prenatal care
- well-baby care
- illnesses and accidents during infancy
- infant development and behavior
Special questionnaire modules also were developed on topics that are of particular importance for understanding the Puerto Rican population, including:
- migration experience
- acculturation
- marriage patterns
- social support
Last modified: 02/13/06 | Contact Webmaster
