Rate

A rate is a measure of some event, disease, or condition in relation to a unit of population, along with some specification of time.  The following rates are defined below
Birth
Death
Fetal death
Infant mortality
Neonatal mortality
Postneonatal mortality
Birth cohort infant mortality
Perinatal mortality
Maternal mortality
Hospital occupancy
Relative survival rate
Fertility
Total fertility rate
Gross reproduction rate
Net reproduction rate
Intrinsic rate of natural increase

A birth rate is calculated by dividing the number of live births in a population in a year by the midyear resident population. For census years, rates are based on unrounded census counts of the resident population, as of April 1. For the noncensus years 1981-89, rates were based on national estimates of the resident population, as of July 1, rounded to 1,000s. Rounded population estimates for 5-year age groups were calculated by summing unrounded population estimates before rounding to 1,000s. Starting in 1991 rates were based on unrounded national population estimates. Beginning in 1997 the birth rate for the maternal age group 45-49 years includes data for mother's age 50-54 years in the numerator and is based on the population of women 45-49 years in the denominator. Birth rates are expressed as the number of live births per 1,000 population.  The rate may be restricted to births to women of specific age, race, marital status, or geographic location (specific rate), or it may be related to the entire population (crude rate). 

A death rate is calculated by dividing the number of deaths in a population in a year by the midyear resident population. For census years, rates are based on unrounded census counts of the resident population, as of April 1. For the noncensus years 1981-89, rates were based on national estimates of the resident population, as of July 1, rounded to 1,000s. Rounded population estimates for 10-year age groups were calculated by summing unrounded population estimates before rounding to 1,000s. Starting in 1991 rates were based on unrounded national population estimates. Rates for the Hispanic and non-Hispanic white populations in each year are based on unrounded State population estimates for States in the Hispanic reporting area. Death rates are expressed as the number of deaths per 100,000 population. The rate may be restricted to deaths in specific age, race, sex, or geographic groups or from specific causes of death (specific rate) or it may be related to the entire population (crude rate).

A fetal death rate is the number of fetal deaths with stated or presumed gestation of 20 weeks or more divided by the sum of  live births plus fetal deaths, per 1,000 live births plus fetal deaths.

A late fetal death rate is the number of fetal deaths with stated or presumed gestation of 28 weeks or more divided by the  sum of live births plus late fetal deaths, per 1,000 live births plus late fetal deaths.

An infant mortality rate is based on period files calculated by dividing the number of infant deaths during a calendar year by the number of live births reported in the same year. It is expressed as the number of infant deaths per 1,000 live births.

A neonatal mortality rate is the number of deaths of children under 28 days of age, per 1,000 live births.

A postneonatal mortality rate is the number of deaths of children that occur between 28 days and 365 days after birth, per 1,000 live births.

Birth cohort infant mortality rates are based on linked birth and infant death files. In contrast to period rates in which the births and infant deaths occur in the same period or calendar year, infant deaths comprising the numerator of a birth cohort rate may have occurred in the same year as, or in the year following the year of birth. The birth cohort infant mortality rate is expressed as the number of infant deaths per 1,000 live births.

Perinatal mortality rate is the sum of late fetal deaths plus infant deaths within 7 days of birth divided by the sum of live births plus late fetal deaths, per 1,000 live births plus late fetal deaths. (Perinatal relates to the period surrounding the birth event. Rates and ratios are based on events reported in a calendar year.) Perinatal mortality ratio is the sum of late fetal deaths plus infant deaths within 7 days of birth divided by  the number of live births, per 1,000 live births.

Maternal mortality rate is defined as the number of maternal deaths per 100,000 live births. The maternal mortality rate is a measure of the likelihood that a pregnant woman will die from maternal causes. The number of live births used in the denominator is a proxy for the population of pregnant women who are at risk of a maternal death.

Hospital occupancy rate is defined by the American Hospital Association as the average daily census divided by the number of hospital beds, cribs, and pediatric bassinets set up and staffed on the last day of the reporting period, expressed as a percent. Average daily census is calculated by dividing the total annual number of inpatients, excluding newborns, by 365 days to derive the number of inpatients receiving care on an average day during the annual reporting period.

Facility occupancy rate for facilities other than hospitals is calculated as the number of residents at the facility reported on the day of the interview divided by the number of reported beds. In the Online Survey Certification and Reporting Database, occupancy is determined as of the day of certification inspection as the total number of residents on that day divided by the total number of beds on that day.

Relative survival rate is the ratio of the observed survival rate for the patient group to the expected survival rate for persons in the general population similar to the patient group with respect to age, sex, race, and calendar year of observation. The 5-year relative survival rate is used to estimate the proportion of cancer patients potentially curable. Because over one-half of all cancers occur in persons 65 years of age and over, many of these individuals die of other causes with no evidence of recurrence of their cancer. Thus, because it is obtained by adjusting observed survival for the normal life expectancy of the general population of the same age, the relative survival rate is an estimate of the chance of surviving the effects of cancer.

Fertility rate is the total number of live births, regardless of age of mother, per 1,000 women of reproductive age, 15-44 years.

SOURCE: Health, United States

Total fertility rate (TFR) shows the potential impact of current fertility patterns on reproduction, that is, completed family size. The TFR indicates the average number of births to a hypothetical cohort of 1,000 women, if they experienced throughout their childbearing years the age-specific birth rates observed in a given year. Because it is based on age-specific birth rates, the TFR is not affected by changes over time in the age composition of a population and can be used to compare populations over time or between different groups.

See Reproduction Rates for 1990-2002 and Intrinsic Rates for 2000-2001: United States for more information.
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Gross reproduction rate (GRR) represents the average number of daughters born to a hypothetical cohort of 1,000 women if they experienced the age-specific birth rates observed in a given year throughout their childbearing years and if none of the cohort was to die during her childbearing years. The GRR is similar to the total fertility rate (TFR) except that it measures only female births, since reproduction is largely dependent on the number of females in a given population. Moreover, like the TFR, the GRR is age adjusted and thus rates can be compared over time or between different groups.

See Reproduction Rates for 1990-2002 and Intrinsic Rates for 2000-2001: United States for more information.
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Net reproduction rate (NRR) is closely related to the gross reproduction rate (GRR).  However, unlike the GRR, the NRR incorporates the effects of mortality.  The NRR represents the average number of daughters who would be born to a hypothetical cohort of 1,000 women, if they passed through their childbearing years conforming to the age-specific fertility and mortality rates of a given year.  In contrast, the GRR assumes that all of the women in the cohort survive through their childbearing years.