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Birth Data Documentation
DefinitionAll data in the birth query pertain to live births. A live birth is defined as the complete expulsion or extraction from its mother of a product of conception, irrespective of the duration of pregnancy, which, after such separation, breathes or shows any evidence of life, such as beating of the heart, pulsation of the umbilical cord, or definite movement of voluntary muscles. The vital statistics term for stillbirths is fetal deaths and they are not included in the birth query.
Sources of Data
BirthsThe birth certificate is the source document for data included in the birth query. New Jersey law requires that the attending physician, midwife, or person acting as midwife file a certificate of birth with the Local Registrar within five days of a birth within the state. Birth records are filed electronically by hospitals. Medical records staff use standard mother and facility worksheets and medical charts to complete the birth registration. Hospital training is provided by the Bureau of Vital Statistics and Registration (BVS). The electronic birth registration system has online edits and records are reviewed by BVS and the Center for Health Statistics (CHS). Additionally, the National Center for Health Statistics provides feedback to BVS on data quality. The state also provides feedback to the hospitals to improve data quality and contacts the hospital staff for clarification of missing, inconsistent, or incorrect entries. The data included in the query are for New Jersey residents regardless of where the birth occurred. The inclusion of statistics on births to New Jersey residents which occurred in other states is made possible through the Vital Statistics Cooperative Program (VSCP), which encourages the exchange of information on vital events between the states of occurrence and residence.
The birth data in the query system were generated from data files available at the time of preparation of the back-end dataset. Any data pertaining to a birth for which a certificate was filed after that time or relating to corrections or revisions made since the data were processed for the electronic file are not included. Vital events computer files are periodically updated by the New Jersey Department of Health's Bureau of Vital Statistics and Registration (BVS) and Center for Health Stastistics (CHS) staff based on correction reports received from local registrars and from data quality control analyses conducted by CHS. The query incorporates data from the most recently updated files.
PopulationPopulation estimates used to calculate birth and fertility rates are derived from the "Bridged-race intercensal population estimates" for 1990-1999 and the most recent vintage of the "Bridged-race postcensal population estimates" prepared by the National Center for Health Statistics (NCHS) in collaboration with the U.S. Bureau of the Census. These estimates result from bridging the 31 race categories used in the 2000 Census, as specified in the 1997 federal OMB standards for the collection of data on race and ethnicity, to the four race categories specified under the 1977 standards. Many data systems, such as birth statistics, are continuing to use the 1977 standards during the transition to full implementation of the 1997 standards. Estimates were developed for each state and its counties by five-year age groups, sex, Hispanic ethnicity, and four race groups (White, Black, Asian and Pacific Islander, and American Indian and Alaska Native). Prior to 2006, municipality population estimates by age, race, ethnicity, and sex were only available in Census years, therefore fertility rates and age- and race/ethnicity-specific birth rates cannot be computed for pre-2006 municipality data. Municipality estimates are provided by the New Jersey Department of Labor and Workforce Development's State Data Center.
Quality of DataThe reporting of births is considered to be essentially complete. According to NCHS, more than 99% of births are registered. The completeness of reporting by residence is dependent on the effective functioning of the interstate data exchange program for certificates which is fostered and encouraged by NCHS. Research has shown that there is some degree of slippage in receiving information on all births of New Jersey residents occurring in other states. However, the number of missing events is thought to be small, relative to the overall number of births.
The quality of the data included in the query is a function of the accuracy and completeness of the information recorded on the respective certificates and of the quality control procedures employed in the coding and keying processes. A query program in which the individual(s) responsible for completing the certificate is questioned about missing or conflicting information is carried out by BVS staff. This process is augmented by the data quality control analyses performed by the CHS using all of the NCHS edit criteria.
In order to participate in the national VSCP, states had to achieve an error rate of 2% or less on each certificate item for three consecutive months. The error rates relate to both coding and data entry errors. New Jersey has met the error tolerance requirements for the cooperative program. After satisfying initial requirements, a monthly sample of records is used to determine that the error rate on each birth certificate item is approximately 4%.
Alcohol, tobacco, and drug use during pregnancy are self-reported by the mother and thus should be interpreted with caution. Reporting of drug use during pregnancy was incomplete before 1996, therefore all maternal drug use data for 1990-1995 are shown as Unknown. Health insurance information was not collected with birth certificate data prior to 1997, therefore all Medicaid status data for 1990-1996 are shown as Unknown. Data on the type of feeding at the time of discharge was not collected prior to 1997, therefore all feeding at discharge data for 1990-1996 are shown as Unknown.
Allocation of Data by Residence or OccurrenceFor public health planning and policy determination, the most useful population to study is usually the resident population of an area. In the case of births, the existence of resident certificate exchange agreements among the registration areas in the country permits analysis of resident birth statistics regardless of where the birth occurred. In the query system, the data presented represent births to New Jersey resident mothers, regardless of where they occurred. Births that occurred in New Jersey to non-NJ residents are not included.
Allocation of births by place of residence within the state is sometimes difficult because classification depends on the statement of the usual place of residence provided by the informant at the time the certificate is completed. For a variety of reasons, the information given may be incorrectly recorded. A common source of error is the confusion of mailing address with residence address. For this reason, all records are run through geocoding software to properly assign the county and municipality of residence.
Race, Ethnicity, and NativityOne race group (White, Black, American Indian/Alaska Native, Chinese, Japanese, Hawaiian, Filipino, Asian Indian, Korean, Samoan, Vietnamese, Guamian, other Asian/Pacific Islander, other race, and an unknown race category) and an ethnicity (Non-Hispanic, Mexican, Puerto Rican, Cuban, Central or South American, other Hispanic, and an unknown ethnicity category) are recorded for each parent of each individual for whom a birth certificate is filed. Race and ethnicity of the child are not recorded and that of the mother is used for statistical analysis. Race and ethnicity can be combined to make a Hispanic "race" group and this is the standard way the New Jersey Department of Health reports birth data.
Due to the limitations of the corresponding population data, race/ethnicity designations used in the birth query are White, Black, Hispanic, Asian/Pacific Islander, and Other Races, where Hispanics may be of any race and the other race groups do not include Hispanics (but include those with ethnicity not stated). The Hispanic category includes persons of Mexican, Puerto Rican, Cuban, Central/South American, or other Hispanic ethnicity, regardless of race. The Asian/Pacific Islander category includes persons of Chinese, Japanese, Hawaiian, Filipino, Asian Indian, Korean, Samoan, Vietnamese, Guamian, and other Asian and Pacific Islander descent who were not reported as Hispanic. The Other Race category includes all race groups other than White, Black, and Asian/Pacific Islander who were not reported as Hispanic. When combining race and ethnicity, Hispanic ethnicity takes precedence over whatever race is recorded for the mother.
Three nativity categories are used in the query: native-born, Puerto Rico-born, and foreign-born. Native-born includes mothers born in the 50 states or Washington, D.C. Foreign-born includes mothers born anywhere other than the 50 states, D.C., and Puerto Rico. Foreign-born, therefore, includes other U.S. territories such as American Samoa, Guam, and U.S. Virgin Islands because all territories are not coded separately in the electronic birth files. Foreign-born also includes those born abroad to American parents because birth certificates do not have an item to distinguish those cases. Numbers of births to New Jersey residents born in territories other than Puerto Rico or born abroad to American parents are extremely small.
RatesThe presentation of birth and fertility rates facilitates comparisons between political subdivisions with populations of different sizes or between subgroups of a population. Crude birth rates are calculated by dividing the number of births to the residents of an area by the resident population of an area or subgroup and are usually expressed per 1,000 residents. Births are limited to those that occur within a specific time period, usually a year, and the population is, in general, the mid-year estimate of the resident population of the area. Fertility, general fertility, and total fertility rates are calculated by dividing the number of births to the residents of an area or demographic subgroup by the female population of that area or subgroup, usually in a specified age range, such as 15-44 years.
In order to compare birth experiences among various ages and races/ethnicities, birth and fertility rates may be computed for subgroups of the population. These are referred to as age- or race/ethnicity-specific rates and are calculated by dividing the number of births within a subgroup by the population in the subgroup.
The definition of rates used in the query system are on the Definitions of Public Health Terms and Acronyms page. It should be noted that alternative forms exist for some of these statistics. Some other states and the federal government may employ different formulae for the computation of selected rates.
Due to the unavailability of detailed municipality population estimates prior to 2006, there is a separate query builder page for municipality birth rates because a different set of population data is used as denominators in the rate calculations. Each query screen is limited to the data available at that geographic level.
Small NumbersCaution should be exercised in the interpretation of rates based on small numbers. Chance variations in the number of births occurring in sparsely populated areas can cause rates to fluctuate widely over time. In accordance with NCHS standards, rates based on fewer than 20 births or fewer than 20 persons in the population are considered unreliable for analysis purposes. Therefore, these rates are not displayed and are indicated by ** in the appropriate cell. For purposes of analyzing birth and fertility rates for small areas, calculation of three- or five-year average rates and other statistical methodologies for analyzing small numbers may provide more meaningful measures.