Explaining breadth of policy engagement: Patterns of interest group mobilization in public policy

How broad do groups spread their engagement across the spectrum of public policy issues? The orthodoxy for some time has been that groups tend to focus their engagement rather narrowly. Some suggest that groups shy away from competition and pursue niche-seeking behaviour. Others argue that resource limitations constrain both the monitoring behaviour of groups and the extent to which groups can engage in policy influence activity. While there is some consensus that groups tend to specialize, there is not a great deal of work that seeks to explain it. To date this question has tended to be explored using survey data alone, which provides generalized findings about 'interest' in policy areas. In this article we go one step further. By linking detailed survey data with the actual policy activity data of interest groups, we investigate the factors that shape the breadth of engagement by interest groups.