at different levels of analysis—from individual behavioral decision theory to systems theory. They focus on different processes: from structural determinism and constrained probabilities at one end of a continuum to willful effort and chance happenings at the other. They draw on epistemologies as varied as positivism, critical realism, and postmodernism. Individual social scientists bring different motivations to their work—from expansion of theoretical knowledge to practical problem solving, from mapping policy options to advocacy of particular policies. Social scientists bring their expertise to universities, think tanks, the media, advocacy groups, corporations, and government agencies. This range—across fields of study and individual motivations and career lines—produces a lot of variability, which, of course, determines the way the science-policy nexus is framed.
Complicating matters is the absence of a generally accepted explanatory model of policy making. Instead, multiple descriptive policy process models offer ways to understand how policy is made and how science might enter into that process. There are, for example, rational models—including linear, cycle or stage, incrementalism, and interactive. There are models that question rational model assumptions, including behavioral economics, path dependency, and bureaucratic inertia. There are political models, including policy networks, agenda setting, policy narratives, advocacy coalition frameworks, punctuated equilibrium theory, and deliberative analysis models (see Baumgartner and Jones, 1993; Hajer and Wagenaar 2003; Kingdon, 1984; Lindblom, 1968; Neilson, 2001; Sabatier, 2007; Sabatier and Jenkins-Smith, 1993; Stone, Maxwell, and Keating, 2001).
There are models that focus on different stages of the policy process and thus on different ways that social science can contribute, including: descriptive analyses that present conditions needing policy attention, such as a slowdown in small business start-ups; social indicators that document long-term trends, such as gender differences in pay scales; social experiments on alternative policy designs, such as school vouchers; and evaluation research on the effectiveness of a policy, such as neighborhood policing.1
Political science is the discipline that has devoted the most attention to the policy process. On the issue of use, it has reached a general conclusion (Henig, in press):
1For a careful discussion of how evidence is used at different stages of the policy process, see McDonnell and Weatherford (2012).