摘要：Public health researchers are addressing new research questions (e.g., effects of environmental tobacco smoke, Hurricane Katrina) for which the randomized controlled trial (RCT) may not be a feasible option. Drawing on the potential outcomes framework (Rubin Causal Model) and Campbellian perspectives, we consider alternative research designs that permit relatively strong causal inferences. In randomized encouragement designs, participants are randomly invited to participate in one of the treatment conditions, but are allowed to decide whether to receive treatment. In quantitative assignment designs, treatment is assigned on the basis of a quantitative measure (e.g., need, merit, risk). In observational studies, treatment assignment is unknown and presumed to be nonrandom. Major threats to the validity of each design and statistical strategies for mitigating those threats are presented. Far better an approximate answer to the right question, which is often vague, than an exact answer to the wrong question, which can always be made precise. —John Tukey 1 THE RANDOMIZED CONTROLLED trial (RCT) has long been the gold standard for clinical research, representing the best way to determine efficacy and effectiveness for many intervention and prevention programs. However, public health researchers are increasingly addressing questions for which the RCT may not be a practical (or ethical) option or for which the RCT can be complemented by alternative designs that enhance generalization to participants and contexts of interest. When structural or policy interventions are being examined, practical problems in conducting RCTs may arise 2 —for example, research participants may not want to be randomized, randomization may not be feasible or not accepted in the research context, or only atypical participants may be willing to be randomized. Such problems might be a concern in studies of the effects of environmental tobacco smoke on non-smokers or of the effects of the severe disruption of Gulf Coast communities by Hurricane Katrina on HIV risk behaviors and medical care. Only atypical participants may agree to participate in the evaluation of a faith-based intervention. Highly religious participants may refuse to be assigned to a non–faith-based treatment group, whereas non-religious participants may refuse or be unable to participate sincerely in a faith-based group. Randomization may be precluded if the religious organization implementing the intervention strongly believes that all people desiring the faith-based intervention should receive it. With one exception, our focus is on designs in which participants are assigned to treatment or control conditions. Parallel designs exist in which settings, time, or even dependent measures are the unit of assignment. 3
