made at the state and federal level, as well as relative to the amount of evaluation research found in other fields, such as medicine, education, or transportation safety. A renewed and greatly expanded commitment to program evaluation of environmental policy would help move environmental decision making closer to an evidence-based practice.

In this paper, we begin by defining the role that empirical analysis can play in policy deliberation and decision making, distinguishing program evaluation research from other types of analysis, including risk assessment, cost-effectiveness analysis, and cost-benefit analysis. Although reliance on these other types of analysis has greatly expanded over the past several decades, most other forms of analysis take place before decisions are made; relatively little analysis takes place after decisions have been made and implemented, which is when program evaluation occurs. We argue that any policy process that takes analysis and deliberation seriously before decisions are made should also take seriously the need for research after decisions are made.

We next explain the kinds of methodological practices that program evaluation researchers should use to isolate the causal effect of a particular regulation or other policy initiative, that is, the change in outcomes that would not have occurred but for the program. Even if an environmental policy is correlated with a particular environmental or social outcome, this does not necessarily mean that there is a causal relationship between the policy initiative and the change in outcomes. Only by adhering to the type of methods we highlight here will researchers be able to isolate the effects of specific policy interventions and thereby inform environmental decision making.

Finally, we suggest that the present time is an especially ripe one for expanding program evaluations of environmental policies. Although program evaluation techniques have been available for decades and have certainly been advocated for use in the field of environmental policy, recent developments in policy innovation, government management, and data availability make the present time more conducive for an expanded program evaluation research agenda. During the past several decades, the U.S. Environmental Protection Agency (EPA) and the states have developed a variety of new approaches to environmental protection that are now ready for evaluation. The prevailing policy climate generally supports evaluation of government performance, as evidenced by the Office of Management and Budget’s new Program Assessment Rating Tool and legislation like the Government Performance and Results Act. Moreover, given the increasing ease of access to data made possible by the Internet, researchers will find it easier today to expand program evaluation in the field of environmental policy. Evidence-based deliberation and decision making over environmen-



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