Cross-sectional studies are usually considered an inappropriate basis for causal inference, particularly so in relation to associations extending over time. Recall bias is an obvious threat. The longer the time interval between initiating drinking and reporting on it, the greater the scope for recall problems and telescoping forward, so as to report a later AFD.7 Adult problem drinkers may also have systematically different recall of their AFD, being more likely to report younger AFD, and/or different willingness to report it from those who do not have such problems.10 These problems also affect case-control studies. Cohort study designs which measure AFD prior to assessment of alcohol related harms provide a stronger basis for investigation of the strength of associations and consideration of possible causation. Particularly where measurement of AFD is soon after the event, they can potentially minimise recall bias and reduce the likelihood of differential reporting problems. A systematic review of cohort studies provides the strongest observational study design to evaluate evidence for causal inference.11 While experimental evidence would be preferable to observational evidence, there is sparse data on the effects of altering AFD due to the intractability of this intervention target.12
