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

Christopher J. Mansfield, PhD

& Satomi Imai, PhD*

East Carolina University

Greenville, NC

134th Annual APHA Meeting

November 4-8, 2006

*Presenter


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Objectives vehicle crash deaths of teens and young adults

  • 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


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Acknowledgement vehicle crash deaths of teens and young adults

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


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Background vehicle crash deaths of teens and young adults

  • 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.


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  • 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)


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  • 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.


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Methods underestimated by conventional definition of mortality rate.

  • 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


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We looked at MVC mortality rates for young drivers in NC by: underestimated by conventional definition of mortality rate.

  • Race/Ethnicity: Whites, African Americans, Native Americans, and Hispanics

  • 41 Eastern Counties

  • Gender: Male vs. Female


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Results underestimated by conventional definition of mortality rate.


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MVC mortality rates underestimated by conventional definition of mortality rate.

per population vs. per licensed drivers


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  • MVC mortality rates underestimated by conventional definition of mortality rate.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





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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


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Regional disparity olds, disparity ratio compared to Whites changes:

Eastern NC vs. the rest of the state


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Regional disparity olds, disparity ratio compared to Whites changes:


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Gender disparity of the state.

  • 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.


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Yearly trend of the state.

2000-2004


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  • 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.


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Teen drivers’ mortality rates increased radically have increased each year regardless of the denominator used.

from 2000 to 2004 (80% increase).


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Limitations have increased each year regardless of the denominator used.

  • 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.


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Conclusions have increased each year regardless of the denominator used.

  • 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.


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  • 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.


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For additional information, 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.

www.chsrd.med.ecu.edu


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