The Statistics of Suicide Don’t be Misled

1. The Statistics of SuicideDon’t be Misled David Lawrence, MPH, RN,CS CSN Injury Data Technical Assistance Center Center for Injury Prevention Policy and Practice Graduate School of Public Health San Diego State University

2. Health Statistics • When looking at the statistics of adverse health outcomes it is important to realize that the numbers refer to individuals with lives, families, and friends. • - - - - - • Health statistics are not like contest scores ... • they should be used to make decisions. • What state has the highest rate of suicide? • - Not particularly useful information • Useful information: • - What groups are most at risk? • - What mechanisms are most used?

3. Death Rate deaths among residents during a calendar year _________________ population at midyear times 100,000 • This is termed the “crude death rate” because it has disadvantages: • It over-summarizes a complex pattern of rates • Lack of comparability for populations which have different age composition

4. Health Statistics • Things happen to people of different ages in different amounts • A state with a larger percentage of people in the age group wherein these things happen will have a higher rate than will a state with a smaller percentage of that age group • If we are to make a “fair comparison” we must adjust or account for these differences between the populations

5. Age Adjustment • Produces a single summary value to compare populations • Eliminate confounding effects of age composition • Weighted average of age-specific values • How to calculate: http://www.InjuryPreventionWeb.org Click on “Injury Data” and then on “Technical Notes”

6. Age-Adjustment • A common practice. Essentially all state-to-state or county-to-county comparisons are made with age-adjusted rates. • Until recently these were made using the 1940 population. • Now, however, the recommended standard is the 2000 population. • Why change?

7. Age-Adjustment • This has important implications for interpretation. • If we age-adjust the California and Alaska suicide rates for 1997 using the 1940 standard population and using the 2000 standard population we will find different rates (10.94 vs. 12.39 and 17.60 vs. 17.42). The new standard increases the adjusted rate for California but decreases it for Alaska.

8. The 1940 Population Was Much Younger Source: US Census Bureau

9. Standard Population Change Using Year 2000 standard: Events occurring to those < 35 will have less weight Events occurring to those > 35 will have more weight

10. Standard Population Change • Although changes in standards are not common they happen now and then • Unemployment Rate • Consumer Price Index • With age adjustment it is possible to follow trends by simply recalculating past years using the new standard.

11. Age-Adjusted Suicide Rate Trends, United States1940 and 2000 Standard Populations Compared Source: WISQARS

12. 1940 Standard Nevada 22.03 Montana 19.01 Wyoming 18.50 New Mexico 18.03 Alaska 17.63 Arizona 16.75 Idaho 16.03 Colorado 15.97 Utah 15.43 Oregon 14.56 2000 Standard Nevada 24.26 Montana 21.27 New Mexico 20.20 Wyoming 18.93 Arizona 18.29 Colorado 17.62 Idaho 17.44 Alaska 17.41 Utah 16.26 Florida 15.89 Suicide Rates* United States, 1990-19971940 and 2000 Standard Populations Compared * per 100,000 population Source: WISQARS

13. Health Statistics • Be careful about the conclusions you draw. • Are you making a legitimate comparison? • Use meaningful statistics • Adjusted rates only adjust for the second, less serious disadvantage to using the crude rate. The most serious problem, oversimplification, the adjusted and crude rates have in common. • Age-specific rates • useful for determining who is at risk • very simple to calculate • may be used without adjustment when making comparisons