Table 2.

Results of Multi-level Poisson Regression Analyses to Assess Intervention Effects on Alcohol-related Motor Vehicle Crashes Among 15 to 30-Year-Old Drivers

Variable	Intent-to-treat Event rate ratio (95% CI)	Dosage level Event rate ratio (95% CI)
Observation level
Time	1.003 (1.00, 1.005) *	1.003 (1.00, 1.005) *
September/October	0.89 (0.82, 0.96) **	0.89 (0.82, 0.96) **
Intervention perioda	0.83 (0.70, 0.98) *	–
<2 DUI operations/quarterb	–	0.73 (0.60, 0.90) **
≥2 DUI operations/quarterb	–	0.87 (0.72, 1.06)
City level
SES factor scorec	0.89 (0.82, 0.97) *	0.89 (0.82, 0.98) *
Percent minority	0.63 (0.27, 1.47)	0.67 (0.28, 1.61)
Population size	0.99 (0.97, 1.02)	0.99 (0.97, 1.02)

Note: Event rate ratios less than 1.0 indicate a lower incidence of alcohol-related crashes during intervention years. The difference from 1.0 represents the percent reduction in the incidence of crashes (e.g., 0.83 represents a 17% reduction in alcohol-related crashes in the 12 intervention cities). Boldface indicates statistical significance

^*p<0.05;

^**p<0.01.

^aFrom April 2013 to March 2016 when high-visibility DUI enforcement operations were taking place in 12 intervention cities compared to the 12 control cities and pre-intervention period for all 24 cities.

^bDUI enforcement operations included sobriety checkpoints and saturation patrols to provide visible enforcement of drink-driving laws. These were accompanied by various types of media (e.g., posters, mobile signs) to raise public awareness of enforcement operations.

^cStandardized factor score based on percent of residents living above poverty, percent employed, percent with a college degree, and median household income.

DUI, driving under the influence.