N C H S - N V S S - Description

The linked birth and infant death data set is a valuable tool for monitoring and exploring the complex interrelationships between infant death and risk factors present at birth. In the linked birth and infant death data set the information from the death certificate is linked to the information from the birth certificate for each infant under 1 year of age who dies in the United States, Puerto Rico, The Virgin Islands, and Guam. The purpose of the linkage is to use the many additional variables available from the birth certificate to conduct more detailed analyses of infant mortality patterns. The linked files include information from the birth certificate such as age, race, and Hispanic origin of the parents, birthweight, period of gestation, plurality, prenatal care usage, maternal education, live birth order, marital status, and maternal smoking, linked to information from the death certificate such as age at death and underlying and multiple cause of death.

Linked files are available for the data years 1983-91 and 1995-2002. Future data years will be available annually. Linked file data were not produced for the 1992-94 data years.

Differences Between Period and Cohort Data
From 1983–91, NCHS produced linked files in a birth cohort format. For the 1991 birth cohort linked file, the numerator consists of deaths to infants born in 1991 whether the death occurred in 1991 or 1992. Beginning with 1995 data, linked files are produced first using a period format and then subsequently using a birth cohort format. For example, for the 1995 period linked file, the numerator consists of all infant deaths occurring in 1995 that have been linked to their corresponding birth certificates, whether the birth occurred in 1995 or in 1994. The denominator for both files is the 1995 natality file, which contains all U.S. births occurring in 1995. The release of linked file data in two different formats allows NCHS to meet customer demands for more timely linked files while still meeting the needs of data users who prefer the birth cohort format. While the birth cohort format has methodological advantages, it creates substantial delays in data availability, since it is necessary to wait until the close of the following data year to include all infant deaths to the birth cohort. Beginning with 1995 data, the period linked file is the basis for all official NCHS linked file statistics (except for special cohort studies).