Estimated trends from the six survey series were widely discrepant. There are many reasons to expect prevalence estimates to vary from survey to survey related to the wording of questions, social desirability bias, differences in survey coverage, and other factors (Tourangeau et al., 2000, Groves et al., 2009). One might reasonably assume that the error induced by these factors is relatively constant from year to year; i.e., that under a given set of measurement conditions, a proportion of people who actually drink will report doing so and that this proportion should be fairly stable over time. This is clearly not the case here: for the larger surveys (NSDUH, NESARC, NHIS, BRFSS), there was no overlap in confidence intervals between any two surveys for full-population trend estimates for either outcome. While this might seem to be a cause for pessimism about alcohol survey research, there are areas of agreement across surveys. For example, estimates of change in both outcomes were consistently more positive for women than for men and for older age groups compared to younger ones. Thus, although there was little consistency in the trend estimates themselves, there was reasonable consistency in the demographic differences among the trends.
