Rate

A measure of some event, disease, or condition in relation to a unit of population, along with some specification of time. (Also see Sources and Definitions, Age adjustment; Population.)

Birth and related rates

Birth rate: 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 1981–1989, rates are based on the midyear resident population, rounded to thousands. Rounded population estimates for 5-year age groups are calculated by summing unrounded population estimates before rounding to thousands. Starting in 1991, rates are based on unrounded national population estimates. (See Sources and Definitions, Population census and population estimates.) Beginning in 1997, the birth rate for the maternal age group 45–49 includes data for mothers aged 45 and over in the numerator and is based on the population of women aged 45–49 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).

Fertility rate: Total number of live births, regardless of the age of the mother, per 1,000 women of reproductive age (aged 15–44). Beginning in 1997, the birth rate for the maternal age group 45–49 includes data for mothers aged 45 and over in the numerator and is based on the population of women aged 45–49 in the denominator.

Death and related rates

Death rate: 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 1981–1989, rates are based on the midyear resident population, rounded to thousands. Rounded population estimates for 10-year age groups are calculated by summing unrounded population estimates before rounding to thousands. Starting in 1991, rates are based on unrounded national population estimates. Rates for the Hispanic and non-Hispanic White populations through 1996 are based on unrounded population estimates for states in the reporting area for a Hispanic-origin item on the death certificate. (Also see Sources and Definitions, Hispanic origin: Mortality file.) Death rates are expressed as the number of deaths per 100,000 resident 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). (Also see Sources and Definitions, Population census and population estimates.)

Visit rate

Visit rate: A basic measure of service use for event-based data. Examples of events include physician office visits with drugs provided, or hospital discharges. In the visit rate calculation, the numerator is the number of estimated events, and the denominator is the corresponding U.S. population estimate for those who possibly could have had events during a given period. The interpretation is that for every person in the population, there were, on average, x events. It does not mean that x people in the population had events, because some people in the population had no events while others had multiple events. The only exception is when an event can occur just once for a person (for example, if an appendectomy is performed during a hospital stay). The visit rate is best used for comparing use across various subgroups of interest, such as age or race groups or geographic regions.