Conceptual Confusion Leads Policy Evaluation Astray

A 2023 Cochrane review of randomized clinical trials (RCTs) of "physical interventions to…reduce the spread of respiratory viruses" 1 generated controversy and confusion in concluding that "wearing masks in the community probably makes little or no difference to the outcome of laboratoryconfirmed influenza/SARS-CoV-2 compared to not wearing masks." 1 Some readers saw proof that "mask mandates were a bust," 2 while others pointed to the engineering and observational research evidence supporting the use of masks. 3This controversy is not only important because it confused policymakers and the public about a prominent tool of pandemic management.It broadly highlights persistent confusion about what policy is and how to measure it.The first task of any policy research is to measure the independent variable, that is, the policy.Although unnoticed in the debate over the Cochrane review, 3,4 none of the studies reviewed involved a mask policy, strictly defined, so the review could not provide any direct evidence on the efficacy of mask laws or public health orders.Mistaking experiments that encourage mask use for