Healthy Kent
Healthy Kent
2020

Community health through community action


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Understanding Infant Mortality Rates


The infant mortality rate is the (annual) number of deaths in infants less than one year of age per every 1,000 live births. The infant mortality rate as generally expressed is not a percentage, and may be easiest to understand in a population where there are exactly 1,000 births annually. In such a case, if 10 infant deaths were reported, the infant mortality rate would be 10.

However, the infant mortality rate can change dramatically based on the total number of babies born, even if the number of deaths stays the same. For example, in a population that has several thousand births annually, the infant mortality rate will be lower than the actual number deaths (i.e., 10 infant deaths in a birth cohort of 5,000 would represent an infant mortality rate of 2).

By contrast, where there are fewer than 1,000 births within a given population, the infant mortality rate will be higher than the actual number of deaths (i.e., 10 infant deaths in a birth cohort of only 750 would represent an infant mortality rate of 13).

Infant mortality rates can also decline even though the actual number of infant deaths has increased. For example, while 10 infant deaths in a birth cohort of 1,000 is an infant mortality rate of 10, if the next year there are 15 infant deaths but 2,000 births, the infant mortality rate would drop to 7.5 although the actual number of infant deaths increased 50%.

Finally, because the number of infant deaths fluctuates from year to year, reporting infant mortality rates in three-year moving averages serves to "smooth" out any wild fluctuations, and is especially useful in compensating for single year anomalies. For example, in 1994 there were 14 black infant deaths in Kent County, while two years later in 1996, there were twice as many, 28. However the 1994-1996 three-year average black infant death rate in Kent County was 18.9 (most years, there are between 18 and 22 black infant deaths in Kent County). Because annual three-year averages help smooth random peaks and valleys, they are also particularly useful in identifying trends over time, such as a true increase or decrease in infant mortality rates.

Health officials have long held that any discussion of infant mortality rates may be more productive when done in the context of the number of deaths and other factors related to birth outcomes and infant morality. In Kent County, few may realize that the number of white infants who die annually is typically twice the number of black infants (for example, according to Michigan Department of Community Health data, in 1999 there were 47 white infant deaths vs. 20 black infant deaths in Kent County. However, there are eight to nine white infants born for every black infant, meaning that infant mortality does affect African American infants at a much higher rate).

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