Policies result from practical arguments that offer reasons for taking a specific policy action (Ball, 1995). These practical deliberations (also referred to as policy arguments; see, e.g., Dunn, 1990; Fischer, 1980; 2007; Manzer, 1984; Marston and Watts, 2003; Stone, 2001) often involve what science says about likely outcomes of different policy choices. As emphasized in Chapter 1, they also involve political considerations insofar as policy choices influence who has and retains power and normative considerations regarding the desirability (or undesirability) of a proposed action, value judgments, and considerations of legitimacy (Esterling, 2004; Gasper, 1996).

Policy arguments have identifiable characteristics. For example, they are based on “a process through which diverse assumptions, interpretations, and contentions are commonly deliberated through an extended critical debate about policy recommendations and other proposals for public action” (Dunn, 1990, p. 324). Policy arguments generally constitute a package of considerations backed by reasons presented to persuade particular audiences of the validity of and need for a given action (Majone, 1989). The arguments consider not just the policy choice at hand, but how that policy interacts over time with many other policies—does opening a charter school in the community decrease or increase housing prices; do housing prices affect the local labor supply; does the labor supply affect whether a chain store locates in the community?

Obviously, it is a complex undertaking to sort out how the multiple characteristics of policy argument function together to yield a coherent, valid, and persuasive argument (Gasper, 1996; Hambrick, 1974; Toulmin, 1969). Although such an appraisal of policy arguments is necessary to understanding how science is used, that exercise is outside the scope of our report. It serves our purposes simply to emphasize that scientific findings, warrants, inferences, data and qualifications attached to these features of science are assembled in policy arguments in more or less compelling, fair, and balanced ways. This raises familiar issues: is relevant science ignored; does the quality and strength of evidence support the policy claims made; is evidence (pro and con) fully presented, etc.

More specifically, understanding how science is used in policy requires investigating what makes for reliable, valid, and compelling policy arguments from the perspective of policy makers and those they need to persuade. For example, arguments that certain consequences will follow from an intervention in a specific circumstance may involve a chain of reasoning

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