Infant mortality represents the health of the most vulnerable age group and can help with interpreting the years of potential life lost (YPLL) rate in a county. Infant mortality is also commonly used to examine global health differences, as well as to understand historic racial inequities in the US.
Infant Mortality is a Rate
Infant Mortality measures the number of deaths among children less than one year of age per 1,000 live births. Rates measure the number of events (i.e., deaths, births, etc.) in a given time period (generally one or more years) divided by the average number of people at risk during that period. Rates help us compare data across counties with different population sizes.
Infant Mortality is a Rare Event (statistically speaking)
Infant death is a relatively rare event in most counties. Counties with smaller populations can see a lot of change in their rates of infant death data from year to year. Such changes are usually due to normal variation and are not necessarily caused by any actual change in the underlying risk of infant death in the county. To help determine if the infant death change in a county is due to normal variation or real change, we recommend examining the provided error margins. Error margins are statistical tools that consider variation in measures. If the error margins overlap year to year, it’s less likely that the variation in infant mortality reflects real underlying changes.
What Deaths Count Toward Infant Mortality?
Deaths are counted in the county where the infant lived. So, even if an infant dies elsewhere in the state, that death is attributed to his/her home county.
Some Data are Suppressed
A missing value is reported for counties with fewer than 20 infant deaths in the time frame.
The numerator is the number of total deaths for infants under one year of age.
The denominator is the total number of live births.
This measure can be used to measure progress with some caveats. Infant mortality is a very long-term health outcome, effects on which might not be seen for years or even decades after a program or policy is implemented. Infant death is also a relatively rare event, especially in small counties. Statistics depend on large numbers of events to detect small changes, and small changes in small communities may be hard to detect. Lastly, it is important to note that the estimate provided in the County Health Rankings is a 7-year average.
Years of Data Used
CDC WONDER mortality data
The Compressed Mortality File (CMF) is a county-level national mortality and population database spanning the years 1968-2017. Compressed Mortality data are updated annually. The number of deaths, crude death rates and age-adjusted death rates can be obtained by place of residence (total U.S., Census region, Census division, state, and county), age group, race (years 1968-1998: White, Black, and Other; years 1999-present: American Indian or Alaska Native, Asian or Pacific Islander, Black or African American, and White), Hispanic origin (years 1968-1998: not available; years 1999-present: Hispanic or Latino, not Hispanic or Latino, Not Stated), gender, year of death, underlying cause of death (years 1968-1978: 4 digit ICD-8 codes and 69 cause-of-death recode; years 1979-1998: 4-digit ICD-9 codes and 72 cause-of-death recode; years 1999-present: 4-digit ICD-10 codes and 113 cause-of-death recode), and urbanization level of residence (years 1968-1998: not available; years 1999-present: per the 2006 or the 2013 NCHS Urban-Rural Classification Scheme for Counties).