Using Drivers' License Records As an Obesity Surveillance Tool: A Surveillance Evaluation in Clark County, Washington

BACKGROUND:   Obesity is one of Clark County’s pressing public health issues as obesity greatly increases the risk for many chronic diseases and lowers life expectancy. Currently, estimates of obesity are measured using the Behavioral Risk Factor Surveillance System (BRFSS), which by design is not meant to estimate obesity below the state level. Other self-reported height and weight measures are often assumed to be biased and previous findings have shown that drivers’ license (DMV) data consistently underestimates weight. However, DMV data has previously trended well with BRFSS data and can be useful demonstrating temporal and spatial patterns at the local level. Following guidance for the evaluation of public health surveillance systems from the Centers for Disease Control and Prevention, we assessed the utility of DMV data for population-based surveillance of obesity at the local level.

METHODS:   We obtained all Washington drivers’ license and state ID card data from the Washington Department of Licensing from 2008 to 2012. This dataset includes age, residence, gender, height, and weight from which we calculated body mass index in kg/m², the standard unit for population-based obesity surveillance. We then compared the distribution of height, weight and age-adjusted obesity in DMV records to BRFSS estimates stratified by year and gender. DMV records were geocoded and aggregated to larger geographic areas to evaluate the spatial distribution of obesity in Clark County. 

RESULTS:   DMV records consistently underestimate the obesity burden in Clark County compared to BRFSS. This difference is especially pronounced in women whose average weight was ten pounds lighter on drivers’ licenses than in BRFSS, compared to five pounds lighter for men. However, DMV records correlate well with BRFSS estimates, provide a more plausible trend than BRFSS estimates, and provide greater spatial resolution than BRFSS estimates. Neighborhood-level estimates from DMV data reveal striking geographic variation in obesity within the county.

CONCLUSIONS:   Despite underreporting obesity DMV records could be a useful tool as the underreporting appears to be consistent. Specifically, DMV records offer better spatial granularity than other sources. Clark County Public Health can highlight disparities at the neighborhood level and can be used to evaluate obesity prevention interventions. DMV records come with significant limitations but can be useful in illustrating health disparities over time and space.