Madsen's lecture, as Senior Visiting Fellow in the Department of Land Economy at the University of Cambridge, has now been posted on the ASI site.
The topic deals with the way in which interest groups impact upon public policy in ways that might be to their own advantage, though not necessarily conducive to the general good. Madsen identifies with the various ways in which they exert influence on legislators. He goes on to show how policies can be crafted to deal with their influence and turn it to advantage if possible, and circumvent it if necessary. He gives examples throughout.
The full text of the lecture can be seen here.