Declining estimated prevalence of alcohol drinking and smoking among young adults nationally: artifacts of sample undercoverage?

A growing concern in public health surveillance surveys that rely on random digit dialing for sampling is the exclusion of adults in cell-phone-only households. The purpose of this study was to examine whether recent increases in wireless substitution have affected estimates of tobacco and alcohol use in the Behavioral Risk Factor Surveillance System (BRFSS) in a subpopulation with notable cell-phone usage (i.e., young adults). BRFSS data from 2001-2005 were examined. Analyses were limited to participants aged 18-24 years, and the sample contained approximately 18,500 persons in each year. Prevalence estimates were generated with SUDAAN software for three health behaviors: cigarette smoking, binge drinking, and heavy alcohol consumption. In addition, the authors examined sample completeness for young adults relative to US Census estimates. Overall, prevalences of all three health behaviors among young adults were fairly stable between 2001 and 2003 but significantly decreased between 2003 and 2005. These trends are not replicated in national surveys that use area probability samples. The authors found a declining trend in the sample completeness ratio for young adults; it declined from 0.32 in 2001 to 0.15 in 2005. Given the high prevalence of wireless substitution among young adults and the declining sample completeness ratio, the authors suspect that the observed decreases in prevalence are artifacts of undercoverage.