Health Event Rates
Quick links to the most current population estimates: US Census Bureau or NJ State Data Center or CDC WONDER.
All three sites have the same estimates but for some users, one site may be easier to use than another.
According to the dictionary, a rate is, "a quantity, amount, or degree of something [numerator], measured per unit of something else [denominator]." In public health, the numerator is the number of people among whom an event occurred during a certain period of time, and the denominator is the total number of people in the population at risk for the same period of time. A rate has four components:
- A specified time period.
- The numerator, the number of people in whom an event occurred during a given period of time, and
- The denominator, the total number of people in the population at risk for the same period of time. This is also referred to as the "person-years at risk."
- A constant. The result of the fraction is usually multiplied by some factor of 10 (such as 100,000), so that the rate may be expressed as a whole number.
In general, a rate is called a "crude rate" if it has not been adjusted for the age, race, ethnicity, sex, or other characteristic composition of a population.
Table 1 shows an example of crude rate calculations for heart disease by sex.
Table 1: Crude Death Rate due to Heart Disease by Sex, New Jersey, 2004
Sex | Number of Deaths | Population Estimate | Crude Death Rate (Deaths per 100,000 Population) |
---|---|---|---|
Male | 9,598 | 4,235,853 | 226.6 |
Female | 10,966 | 4,463,026 | 245.7 |
Using the values, above, for males as an example...
- The specified time period is 2004.
- The numerator, or the number of events, was 9,598.
- The denominator, or the estimated population at risk, was the July 1, 2004 population estimate of 4,235,853.
- The constant was 100,000.
The calculation for the crude death rate due to heart disease among males for 2004 looks like this:
FAQs for Crude Rates:
Combining Years
The calculation for an age-specific rate is the same as for a crude rate.
Table 2: Suicide Mortality Rates by Age and Sex, New Jersey, 2004
Male | Female | |||||
---|---|---|---|---|---|---|
Age Group | Suicide Deaths | Population | Age- and Sex-Specific Rate per 100,000 Population | Suicide Deaths | Population | Age- and Sex-Specific Rate per 100,000 Population |
<15 | 5 | 897,553 | ** | 1 | 855,569 | ** |
15-44 | 250 | 1,821,036 | 13.7 | 56 | 1,792,745 | 3.1 |
45-64 | 155 | 1,038,488 | 14.9 | 37 | 1,112,479 | 3.3 |
65+ | 73 | 456,880 | 16.0 | 21 | 666,485 | 3.2 |
** Number is too small to calculate a reliable rate. |
Age-specific rates are valuable for comparing rates across age groups, and crude rates provide a useful summary measure to compare similar populations of different sizes, but the word "similar" is a key concept. It can be misleading to compare crude rates across populations that have relevant differences, such as different cultural traditions, or age, race/ethnicity, or sex composition.
One difference that is commonly controlled for statistically is age composition of the population. The crude mortality rate for a population depends on the mortality rate in each age group as well as on the proportion of people in each age group. For instance, the age-specific rate for most causes of death will be higher for older age groups. As a result, crude death rates tend to be higher in populations with a larger proportion of older persons, and lower in populations with a larger proportion of younger persons.
An age-adjusted rate is a summary measure that may be used to compare mortality or disease risk in two populations with different age compositions.
If you're calculating a rate for: | Then use: | ||
---|---|---|---|
Table/Dataset | File Name | ||
NEW JERSEY | |||
Total population | State Population Totals | NST-ESTyyyy-POP | |
By characteristics | Age, Sex, Race, and Hispanic Origin - 6 race groups | SC-ESTyyyy-ALLDATA6 | |
COUNTIES | |||
Total population | County Population Totals | CO-ESTyyyy-POP | |
By characteristics | Age, Sex, Race, and Hispanic Origin | CC-ESTyyyy-ALLDATA | |
MUNICIPALITIES | |||
Total population | Minor Civil Divisions | SUB-MCD-ESTyyyy-POP | |
By characteristics | Go to data.census.gov. The ACS term for municipalities is "county subdivision." |
yyyy = The most recent year available for the table or dataset
Always use the July 1 estimate from the year(s) that corresponds to your numerator.
If the question is: | Then use: |
---|---|
MAGNITUDE: How big is the problem? | Number of events (count) |
PROBABILITY: What is the underlying risk in a population? | Crude rate and confidence interval |
DISPARITY: Is there a difference in risk after controlling for age? | Age-adjusted rate and confidence interval |