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Mortality Dataset :: Frequently Asked Questions

What are ICD codes?

International Classification of Diseases ICD (ICD-10) codes are used to signify causes of death in death certificate data files. In order to search for mortality rates or raw numbers of deaths from a condition not listed in the menu, you will have to specify the ICD codes that are used to indicate the specific condition you are interested in. In order to identify ICD codes for the condition that interests you, click here.


What are age-adjusted mortality rates?

Age-adjustment is typically performed when we are comparing two or more groups or regions that have different age distributions. For example, one population may have a greater proportion of younger people than another population. If age is associated with mortality due to the outcome of interest (i.e., younger or older people are more likely to die from the outcome) it may not be valid to compare crude mortality rates (rates that ignore the age structure of the populations). This point is best illustrated with a simple example.

Population A Population B
  Age Deaths Population Rate per 100K Age Deaths Population Rate per 100K
  Young 50 1,000,000 5.0 Young 150 3,000,000 5.0
  Middle 200 2,000,000 10.0 Middle 200 2,000,000 10.0
  Old 600 3,000,000 20.0 Old 200 1,000,000 20.0
  Total 850 6,000,000 14.2 Total 550 6,000,000 9.2

In both Population A and Population B each age group has the same mortality rate: 5 deaths per 100,000 for young people, 10 deaths per 100,000 for middle age people, and 20 deaths per 100,000 for older people. The total rate in population A, 14.2 deaths per 100,000 is higher than in Population B, 9.2 per 100,000. Although the age-specific rates are the same in each population, Population A has 3 times as many old people as Population B (3,000,000 vs. 1,000,000). Since the age structure of these two populations is different and mortality is different across age groups (higher rates occur among older people) it is not valid to compare the rates in Population A and Population B without accounting for age. We can accomplish this by age-adjusting the rates using standardization. This involves applying the age-specific rates observed in each population to the age distribution of a standard population. Thus, age-adjusted rates are a weighted average of the age-specific rates, with the weighting structure coming from a predefined standard population. In essence, we are asking, “What would the overall mortality rate be in a population with the age structure of the standard population if it experienced the age specific rates of Population A or Population B?”

Population A Population B Standard Population
  Age Rate per 100K Age Rate per 100K Population Size
  Young 5.0 Young 5.0 2,000,000
  Middle 10.0 Middle 10.0 2,000,000
  Old 20.0 Old 20.0 2,000,000
  Total 14.2 Total 9.2 6,000,000

Population A Age-Adjusted Rate:
[(5.0*2,000,000) + (10.0*2,000,000) + (20.0*2,000,000)] / (2,000,000 + 2,000,000 + 2,000,000) = 
11.7 deaths per 100,000 persons

Population B Age-Adjusted Rate:
[(5.0*2,000,000) + (10.0*2,000,000) + (20.0*2,000,000)] / (2,000,000 + 2,000,000 + 2,000,000) = 
11.7 deaths per 100,000 persons

So by applying the age-specific mortality rates in these two populations to the same standard population it becomes apparent that, after accounting for differences in the age structure of the populations, the mortality rates are the same. While this example was somewhat simplified, it is the same procedure used to age-adjust mortality rates in the data query system. The major difference is that the US 2000 Standard Population is used as the standard in the query system. This standard population has 11 age categories and represents the age distribution of the total U.S. population in the year 2000.

Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.
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