[T]he main thrust of the political science literature serves as a warning against idealized visions of pure data being applied in depoliticized arenas. Although generalizations about an entire discipline inevitably are oversimplifications, the center of gravity within the field encourages skepticism about proposals for a rational, comprehensive, science of public policy making and regards data and information as sources of power first and foremost.
It is difficult to assess how widely this characterization is accepted outside of political science, but it is clear that the various models and frameworks do not coalesce into anything remotely resembling a powerfully predictive, coherent theory of policy making. Lacking that, it is improbable and perhaps impossible to reach a widely agreed-upon understanding of the use of science in policy making. “Use” itself, consequently, is elusive, seen differently depending on the perspectives brought to it and the policy and institutional arenas in which it is investigated (Neilson, 2001; Webber, 1991; Weiss, 1991). A political psychologist at the Central Intelligence Agency concerned with what transforms an angry, unemployed teenager into a terrorist uses research evidence very differently from an economist at the RAND Corporation designing a randomized controlled field trial (RCFT) on classroom size and school performance. Many researchers underscore the conceptual confusion about use and conclude that different definitions of use are needed and appropriate for different purposes (e.g., Oh, 1997; Rich, 1997; Weiss, 1979).
This conclusion is consistent with the fact that policy choices are context dependent. A school district deciding whether to establish charter schools is less interested in a comparative study of charter and public schools across the country than in wanting to know how well a charter school will perform under its conditions, which differ depending on whether the district is in the central city or suburb, with a homogenous or diverse population, with a historically competent or incompetent school administration. The usefulness of research is not assessed in terms of variance explained from a large sample of schools, but whether it is informative about a very specific choice.
Given the context-dependent nature of the use of science, typologies are a common way of mapping the landscape (for a summary, see Nutley et al., 2007; see also Bogenschneider and Corbett, 2010; Renn, 1995). A frequently cited typology is that of Weiss (1979, 1998; see also Weiss et al., 2005):