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Calculating a Rate
It is customary to use rates per 100,000 population for deaths and rates per 1, population for live births.
To calculate the rate for deaths from injuries and poisoning for Allen County in 2000, do the following calculation:
There may or may not be 100,000 residents in the county under review, but multiplying the result by 100,000 makes that rate comparable with counties with more than 100, or less than 100,000 (such as Bartholomew County).
Make sure you use the same population base when calculating rates for comparison. For comparing Allen County with Bartholomew County, use the 2000 population estimates for each population base. Population data can come from the Census Bureau
( www.census.gov) or the Indiana Business Research Center ( www.stats.indiana.edu/ ).
Another example is the number of deaths from communicable diseases is 18 per 100,000. A rate of 18 per 100,000 is not 18 percent, but .018 percent. To make a rate into a percent, for the example of 18 deaths per 100,000 population, divide by 1,000:
Be careful about the decimal point. This formula cannot be used with age- adjusted rates. Be very clear about the denominator.
Age/Race-Specific Rates
For particular age, race or sex groups, you can calculate a rate for that specific group. For example, to calculate the 2000 birth rate for white females age 20-24 for Marion County, do the following calculation:
The same calculation can be used for the black birth rate (number of live births to black females divided by the population of black females age 15- multiplied by 1,000). The calculation can also be used for the sex-specific rate of heart disease to males age 65-74 (number of deaths from heart disease to males age 65- divided by the population of males age 65-74 - remember to use the same years for deaths and population - multiplied by 100,000.
Age-Adjusted Rates
The age-adjusted death rate is a good way to compare death rates between counties, states and the U.S. The Epidemiology Resource Center at the Indiana State Department of Health uses the direct method to age-adjust. In this method, the age- specific rates are first calculated for the various age groups (e.g. <1, 1-4, 5-14, 15-24, etc.). An example of an age-specific death rate would be the total number of deaths for residents age 15-24 divided by the population for that age group then multiplied by 100,000 (use the same year for the number of deaths and population). The age-specific rates are then weighted according to the standard million. The standard million is the proportion of the total U.S. population for the same age groups used to determine the age-specific death rates. The year 2000 standard million is used in ERC mortality reports for 1999 forward. Prior to 1990, the 1940 standard million was used. After each age-specific rate is multiplied (weighted) according to the standard million, the age- specific rates are added together, and the sum of each of those weighted rates equals the age-adjusted death rate. Deaths of unknown age are not included. An example is below:
Age
Group
standard
million
Indiana
population
CAUSE
OF
DEATH
(all causes
used)
Age-specific
death rate
age-specific
death rate x
standard
million
Total 1.000000 6,004,813 55,209 930.
*The number in red is the age-adjusted death rate.
Two counties may each have an identical number of deaths; however, the age-adjusted death rates would not be the same unless the deceased were the same age and the population data were the same..
An age-adjusted death rate can be calculated for all causes of death (total) or individual causes, as is done in Tables 1 and 5 in the Mortality Report.
An option when dealing with small numerators is to combine years of data. Using the infant death information from the example above, a three-year rate is calculated:
The numerator is now 30 and the rate is more stable.
Percentage Change
To figure the percentage change, for example, Indiana's population from 1990 to 2000, use the following calculation:
The percentage change calculation will also work if there is a decrease from one year to the next. For example, to figure the percentage decrease in infant deaths for Indiana from 1996 to 2000:
Percent changes aren't always useful. For example, a county newspaper reports that drowning deaths to children age 5-14 has increased 300% in the past year. This increase appears to be appalling, but is it? The information is below:
Again, the numerator is less than 20. Changes in small numbers can lead to large, but meaningless, increases or decreases to the percent change.
Keep in mind that sometimes the most current information is "provisional," which means the data are not final and are incomplete. Provisional means that some numbers and rates may change when the data are final. Therefore, caution should be used in interpreting the data, and you may want to wait until the final data are released. Provisional data are released in order to help organizations that use vital statistics data begin looking at the most current year available.
