Abstract

Nancy is ultimately most concerned about how to determine the relevance of evidence to implementation of evidence-based policy guidelines, in other words, the transferability of study results to a population different from the one that was studied and in which procedures or conditions are not the same as those in the study. And she is concerned about the privileged position Randomized Controlled Trials (RCTs) are given in the ranking schemes for evidence-based policy, because as she sees it RCTs do not address this question while other methods do. RCTs are highly regarded because of their strength in ruling out confounding variables, but they can be weak on the transferability problem because the manipulations necessary for controlled experiment also guarantee that the setting and population are different from the situation and population targeted for application. However, both of these familiar points are simplifications that can be misleading. Some non-RCT type studies (e.g. soft interventions) can also be very good at ruling out confounding variables.1 And, as I will explain, the problems leading to the transferability problem – interacting variables and a difference between study and target populations – are present in any study, not unique to RCTs. In addition