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Choice of denominator to measure disparities in motor vehicle crash deaths of teens and young adults

Choice of denominator to measure disparities in motor vehicle crash deaths of teens and young adults Christopher J. Mansfield, PhD & Satomi Imai, PhD* East Carolina University Greenville, NC 134th Annual APHA Meeting November 4-8, 2006 * Presenter Objectives

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Choice of denominator to measure disparities in motor vehicle crash deaths of teens and young adults

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  1. Choice of denominator to measure disparities in motor vehicle crash deaths of teens and young adults Christopher J. Mansfield, PhD & Satomi Imai, PhD* East Carolina University Greenville, NC 134th Annual APHA Meeting November 4-8, 2006 *Presenter

  2. Objectives • Examine regional, racial/ethnic, and gender disparities in motor vehicle crash deaths for teens and young adults in North Carolina. • Compare motor vehicle crash (MVC) mortality rates for the young drivers using two measures - per population and per licensed drivers • Identify vulnerable populations to whom interventions should be targeted for motor vehicle crash deaths

  3. Acknowledgement Center for Highway Research, UNC Chapel Hill for data on the number of young licensed drivers in NC.

  4. Background • Over the past 5 years, 24% of drivers and 30% of passengers who died in motor vehicle crushes in NC were ages 16-24. The number of deaths is highly disproportionate considering this age group represents 12% of the total population. • Mortality rates due to MVC for ages, 16-24, have increased since 2000 in NC despite the enactment of graduated licensing law. • Healthy People 2010 and Healthy Carolinians 2010 have not identified disparities as specific problems to be addressed for young deaths by MVC.

  5. Typically, MVC mortality rates are expressed as deaths per population (e.g., Healthy People 2010). • However, risks for fatal crashes may differ according to age, race/ethnicity, and region for young population because of varied exposure to motor vehicles. • Age: Teens (15-19) drive fewer miles than 20-24 yr olds, who drive fewer miles than 25-54 yr olds. • Race: African Americans drive less than whites (2001 National Household Travel Survey)

  6. Miles or hours driven is an appropriate denominator to examine MVC mortality risk for young drivers. • 19 year-olds had a highest MVC mortality rate per population, but • 16 year-olds’ MVC mortality rate per 100 million vehicle miles traveled was 1.4 times higher than 18 yr olds’ and 2.2 times higher than 20-24 yr olds’. (Fatality facts 2004, Insurance Institute for Highway Safety) • However, data on miles driven at the state/county level by race/ethnicity are not available. • An alternative: The number of licensed drivers for the denominator.

  7. We suspect that disparities by race/ethnicity exist but are underestimated by conventional definition of mortality rate. • We compare here the difference in young adult MVC mortality rates calculated per population to rates per licensed drivers in NC by race/ethnicity, region, and gender.

  8. Methods • Analyzed MVC death data in NC for ages 16-24 for a 5-year period, 2000-2004 *from the North Carolina State Center for Health Statistics • MVC mortality rates • Per 100,000 population *from the National Center for Health Statistics • Per 100,000 NC licensed drivers *from the UNC Highway Safety Research Center

  9. We looked at MVC mortality rates for young drivers in NC by: • Race/Ethnicity: Whites, African Americans, Native Americans, and Hispanics • 41 Eastern Counties • Gender: Male vs. Female

  10. Results

  11. MVC mortality rates per population vs. per licensed drivers

  12. MVC mortality rates per population • Peak at age 19, then gradual decline to age 24. • MVC mortality rates per licensed drivers • Highest at 16 yrs old, drop at age 17, gradual decline to age 24. • The use of mortality rates per population underestimates the MVC death risks for teen drivers

  13. Racial/ethnic disparities assessed by different mortality rate definitions

  14. Substantial differences, particularly for Native Americans.

  15. Disparities are much more substantial when measured by the licensed driver rate

  16. When using Licensed Drivers as the denominator, for 17 year olds, disparity ratio compared to Whites changes: Native Americans – from 3.5:1 to 8.1:1 Hispanics – from 0.8:1 to 5.5:1 African-American – from 0.5:1 to 1.3:1

  17. Regional disparity Eastern NC vs. the rest of the state

  18. Regional disparity

  19. Eastern NC has much higher MVC mortality rates than the rest of the state. • Minority drivers in eastern NC are particularly vulnerable to MVC deaths. • MVC mortality rates for Native American and Hispanic drivers in eastern NC were more than two times higher than white drivers in the same region.

  20. Gender disparity • 2.7 times more males (1256) died of MVC than females (470) in NC, 2000-2004. • Males and females have similar rates of obtaining a driver’s license, thus gender disparity is comparable between mortality rates per population and per licensed driver.

  21. Yearly trend 2000-2004

  22. Since 2000, MVC crash mortality rates of young drivers in NC have increased each year regardless of the denominator used. • 2004 marked the highest mortality rate per licensed drivers in the past 5 years, 45% increase from 2000 in eastern NC and 24% increase from 2000 in NC. • MVC mortality rates for teen drivers, especially 16 yr old drivers, have been increasing since 2000.

  23. Teen drivers’ mortality rates increased radically from 2000 to 2004 (80% increase).

  24. Limitations • Caution is needed for the interpretation of results in this presentation. • The data might not be reliable due to the small number of deaths among Native American and Hispanic drivers. • Accuracy of reporting race/ethnicity in death records. • Accuracy of population estimates for minority populations, especially Hispanics.

  25. Conclusions • MVC mortality rates per licensed drivers for young drivers show wider disparities by race/ethnicity and region than those per population. • MVC death risk for teen and minority drivers is underestimated by the use of mortality rate per population.

  26. In particular, 16 year-old drivers, and young Native American and Hispanic drivers had tragically high rates for MVC deaths. Young African American drivers had a similar MVC mortality rate to young white drivers when licensed drivers were used as the denominator. • Despite the enactment of the graduated licensing law, the mortality rate for 16 year old drivers has increased.

  27. For additional information, www.chsrd.med.ecu.edu

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