What is a mortality rate?
A mortality rate is a common concept used in health policy. It reflects how many people have died of a certain cause per unit of population (often per 100,000 residents) over a specific period (often a year, or a decade).
Examples of mortality rates
For example, the CDC reports an opioid mortality rate per 100,000 population for 2013-2017.
Let us look at two urban counties in Georgia, the state of Georgia, and the USA as a whole:
Fulton County, GA has a population of 1,011,187.
Newton County, GA has a population of 105,334.
The state of Georgia has a population of 9,251,671.
The United States has a population of 201,155,028.
Fulton County has an opioid mortality rate of 8.4 per 100,000 population.
Newton County has an opioid mortality rate of 6.9 per 100,000 population.
The state of Georgia has an opioid mortality rate of 8.46 per 100,000 population.
The United States has an opioid mortality rate of 10.9 per 100,000 population.
Why is mortality rate useful?
With the examples above, we can see why the mortality rate is useful. The mortality rate allows you to compare across counties, states, and countries, even though their populations are very different. If we would only have the exact amount of people who have died, we would have a difficult time comparing these rates. That is why mortality rates are very useful measures for researchers, policymakers, and others.
When is mortality rate less useful?
A mortality rate can be less useful with small populations.
For example, let’s pick Bacon, GA. This rural county has 11,279 residents. The CDC does not show their opioid mortality rate. Why? We want to compare the mortality rate for opioid with the others, so we would need it per 100,000 population. However, each resident for Bacon County would count for about 8.87 people (11,279 divided by 100,000).
Say one single person died in Bacon County of an opioid overdose. The mortality rate would jump to 8.87 per 100,000 population. Say two people had died in Bacon County. The mortality rate is now around 17.5 per 100,000 population. This is much higher than Fulton County, Newton County, the state of Georgia, and the US! Policymakers might think that something very serious is going on in Bacon County. But only two people have died! To be clear, this is simply an example, and we do not know how many have actually died.
An opioid mortality rate per 100,000 population would be less useful for a small county such as Bacon County, GA. For that reason, the CDC often does not show mortality rates for smaller counties. They will mark this as “suppressed” in their data, or “not available”, or “no data”.
Mortality rates can be absent for smaller counties. Their smaller population will increase the mortality measure for each death with a very high number. This would make the mortality rate seem out of control, when the actual problem might be very small.