IRCPPS in the Links: How Influential are Public Interest Groups?

The Monkey Cage ponders the question:

...Categorizing groups as representing the “public interest” is tricky.  Even among groups typically considered “public interest groups,” a few relatively large and well-established organizations account for the bulk of opportunities for influence, such as media appearances and committee testimony. And these groups may only represent the interests of their most advantaged constituencies, ignoring the issue concerns of disadvantaged subgroups of their constituencies. “Public interest groups,” in other words, represent small portions of the public....