with many associations plausibly reflecting effects of selectivity. However, when cross-sectional survey data are used in pseudo-prospective survival analyses with time-dependent covariates, the results may be as valid as those from prospective studies with short follow-up intervals. That is, the advantages of having a fixed follow-up interval for individuals who are alcohol dependent at a single point in time may be outweighed by the advantages of being able to examine longer intervals of varying lengths among individuals who were ever dependent at any time in their lives. Although a prospective survey that incorporated multiple follow-up measurements over a long interval for a nationally representative sample would appear to offer the advantages of both types of study design, such an approach is highly resource-intensive, and multiple follow-up interviews may decrease the ultimate rate of retention. Finally, it is important to bear in mind that longer observation periods, regardless of whether prospectively or retrospective ascertained, always introduce issues of selectivity and attrition that must be borne in mind when interpreting correlates of recovery.
