Infant Mortality Technical Notes
Infant Mortality:
Infants are fined as all children within 365 days of date of birth or under 1 year of age.
Infant mortality is defined as the number of resident infant deaths per 1,000 resident live births for a particular year.
Race and Ethnicity Considerations:
The terms white, nonwhite, other races and minority designate racial status. The term Hispanic denotes ethnicity. Hispanics
can be of any race are therefore included in the denominator for both white and other races (minority/nonwhite) categories. However,
In Mecklenburg County, the majority of Hispanics fall into the white racial category, therefore, if only 2 population categories, white
and non-white (minority or other races), are available, it is erroneous to assume the non-white rates are heavily influenced by
Hispanics.
In order to best compare Hispanics to other racial groups, it is necessary to sort out Non-Hispanic groups whether they are
white, black, Asian, American Indian or other, and when these data are available such a comparison can be made (i.e. Hispanic rates
are compared to Non-Hispanic white or Non-Hispanic black rates). Such comparisons can be made for infant deaths because the rates
are based on the number of live births for which data is available for each Non-Hispanic racial category and Hispanics.
Small Number of Events and Caution When Interpreting Infant Mortality Rates
The term “rate” refers to the number of vital events (i.e. births, deaths, pregnancies etc.) in a given period of time (i.e. 2003 or
2001-2003) divided by the average number of people at risk during that period (i.e. July 1st average population estimate during that
time period). For example, the infant mortality rate represents the number of infants less than 1 year of age at risk of dying before the
age of 1 year (or years) of all the infants born in a given time period or specific year.
It is often the case when infant mortality rates are examined on a local level (i.e. city or county) by race and ethnicity that the
rate is based on a small number of deaths (less than 20 events). Any death rate with less than 20 events in the numerator will have
substantial random variation over time (a large standard error) and are subject to serious random error. Therefore, extreme caution
should be taken when making comparisons or assessing trends with rates based on less than 20 events. When assessing trends in infant
mortality rates that are race/ethnic specific and based on small numbers, the emphasis should be placed on the number of deaths or
percentage of deaths out of the total number of deaths rather than the rates.
Annual infant mortality rates as a whole or by broad race categories such and White and Minority are more stable than rates by
ethnicity because they are based on greater than 20 events and the amount of random error associated with the rate is significantly
reduced. When examining infant mortality rates by race and ethnicity you are dividing up the events into smaller subgroups and for
populations with a total number of deaths less than 20, the amount of random error increases making the rate unstable. Although the
number of Hispanic births in Mecklenburg County has been increasing by an average of 2 percentage points per year since 1998, the
number of Hispanic infant deaths is still less than 20 per year making the infant mortality rate for this population unstable and subject
to random error. As a population grows it is normal to expect more deaths within that population over time.
Source: NC DHHS/State Center for Health Statistics
Prepared by the Mecklenburg County Health Department, Epidemiology Program, October 2009