What gets measured, gets changed: evaluating law and policy for maximum impact.

21 Does law matter regarding public health outcomes? Regardless of what one may think about the answer to this age-old question, in recent years the public health community has increasingly demonstrated and recognized the roles that public health laws and policies play in effectuating longlasting and broad-based population-wide changes.1 Public health laws and policies have been instrumental in the following ways: reducing smoking prevalence; reducing underage alcohol-related drinking, driving, crashes, and fatalities; reducing exposure to secondhand smoke; eliminating vaccine–associated paralytic poliomyelitis (VAPP); increasing seat-belt use and reducing traffic fatalities; reducing dental carries; and reducing access to and consumption of unhealthy foods and beverages sold in schools and to reductions in caloric intake and overweight.2 In fact, in a review of the ten greatest public health achievements in the 20th century, all were influenced by policy change.3 While there are decades of evidence as to the role that public health law and policy play in improving societal health, literature on the need for and the “art and science” of conducting systematic law and policy surveillance and evaluation research has only recently emerged.4 In this article, we briefly discuss: (1) the need for and relevance of conducting systematic policy surveillance and evaluation; (2) factors to consider when measuring or evaluating laws and policies; and (3) examples of how policy impact studies have informed policy debates and decision-making.