It is unlikely that response or other biases completely account for the strong trends observed here. In this study, there were contrasting cohort trends across different drug types, suggesting that a uniform bias or pattern of “forgetting” did not apply. Similar birth cohort trends in age of initiation of illegal drug use have been observed in other epidemiological studies in the US [51,52] and Australia [53], some of which used data collected across time (rather than relying solely on retrospective reports; e.g., see [51]).
