Social inequality in motorcycle helmet use: when a reduction in inequality is not necessarily good news

BACKGROUND: We sought to examine changes in the magnitude of social inequality in motorcycle helmet use in Taiwan between 2001 and 2009. METHODS: Using data from the 2001 and 2009 Taiwan National Health Interview Surveys, we calculated absolute (the slope index of inequality, SII) and relative (relative index of inequality, RII) measures of inequality in helmet use by three indicators of socioeconomic position. RESULTS: The rate of motorcycle helmet use was 92% (14 801/16 100) in 2001 and decreased to 89% (15 748/17 948) in 2009. We noted a significant decrease in social inequality in helmet use in RII according to urbanisation level, a significant decrease in SII and RII according to income level, and a significant increase in SII according to education level. The reduction in RII according to urbanisation level was more prominent than that based on income level, from 1.73 (95% CI 1.63 to 1.84) in 2001 to 1.33 (95% CI 1.27 to 1.39) in 2009. The decline in helmet use was most prominent for motorcycle users who live in suburban areas, from 94% in 2001 to 88% in 2009. CONCLUSIONS: The significant reduction of social inequality in helmet use according to urbanisation level and income is not a public health success story. Rather, it is a warning sign of slackening law enforcement in Taiwan.