Bentley's (1908) research offered preliminary insights on how advocacy groups affect the policy process. After Bentley's research, numerous studies on interest groups followed, with each study revealing the importance of interest groups to the policymaking process and the difficulty of measuring the impact of interest group influence on the policymaking process (Baumgartner & Leech, 1998, p. 45-46).
In addition to interest groups, political scientists also emphasized the role of bureaucrats, policymakers, and the media in the policy process. All of these entities could influence a specific policy subsystem such as agricultural subsidy policy, pesticide regulatory policy, or any policy considered by policymakers. Over the course of 100 years, political scientists used case studies and quantitative analyses to further examine the impact of these variables on the policy process. By the late 1980s, this collection of research helped to provide the theoretical backdrop to models such as the ACF and PE that attempted to theorize about policy process.
The ACF owes much of its intellectual heritage to research on the impact of interest groups on the policy process. This line of research started in the early 1900s and can be roughly divided into four eras. In the first era, lasting from 1900- 1930s, researchers examined the pressure tactics of groups and the impact of those tactics on the policy process. Significant works during this era included Arthur Bentley's (1908) The Process of Government. Bentley broadly theorized that groups compete against one another in order to influence governmental processes (p. 222,269). Although Bentley was not concerned with constructing specific theories on group activity, his research was the first to suggest that groups influenced the policy process. It also helped political scientists refocus their research efforts to other aspects of government aside from legalistic examinations of governing institutions (Bentley, 1908, p. 162).
Similar works that examined the role of interest groups, or pressure groups as they were commonly known during this period, followed with each work examining the importance of interest groups in policymaking and reconciling that notion with theories of government and democracy (Griffith, 1939; Herring, 1929; Odegard, 1928; Schattschneider, 193 5; see also Cleveland, 19 13; Crawford, 1939; Croly, 19 15; Pollock, 1927; Zeller, 1937). Even more than Arthur Bentley, whose work was generally not even recognized until the 1950s, these researchers made the study of interest groups' impact on the policy process noteworthy (Garson, 1978, p. 77). However, it was not until the 1950s that interest group research really became important to political science. During this second era of research, lasting approximately from the 1940s- 1960s, the study of interest group influence on the policy process reached its scholarly zenith as the administrative size of the federal government increased. Research during this time period reaffirmed the importance of interest groups to policymaking (Griffith, 195 1 ; Latham, 1952; Truman, 1951 ; see also Key, 1952; McConnell, 1966). Some of the most influential research also extended the notion of interest group influence on the policy process to the notion that interest groups, policymakers, and agencies jointly controlled the policy proc