Oguzhan Dincer and Michael Johnston have posted this draft on SSRN.  Here is the abstract:

Using data from the “Edmond J. Safra Center for Ethics Corruption in America Survey”, we construct indices measuring two specific forms of corruption across American states: illegal and legal. We define illegal corruption as the private gains in the form of cash or gifts by a government official, in exchange for providing specific benefits to private individuals or groups, and legal corruption as the political gains in the form of campaign contributions or endorsements by a government official, in exchange for providing specific benefits to private individuals or groups, be it by explicit or implicit understanding. We then put our indices to work and investigate why some states are more corrupt than the others. In addition to demographic and economic variables we also investigate how political participation effects corruption depending on how well it is covered by the media. Our results suggest that we have a lot to learn about the politics of corruption control.

I’m working on a paper on this topic posting soon, reaching similar conclusions.  Looking forward to reading this.