It's round two! On the issue of incumbency, we are in heated agreement that incumbents are different from you and me. So I'll leave it at that.
On the contribution limits study, Ciara states this:
(Incidentally, as to the critique of our analysis vis-à-vis gerrymandering, to the extent that some states have stricter gerrymandering rules than others, Dr. Stratmann controlled for this with state dummy variables. He also controlled for other factors as well to rule out the problem of endogeneity.)
The Stratmann study says this (I added the boldface):
State dummy variables (fixed effects) control for differences across states that are constant within the state over time (1980-2006) but that may influence all of the aforementioned measures of competitiveness. To the extent that these state dummies account for time invariant variables, such as the number of districts, they do not need to be included in the regression equation because the state dummies already control for these variables. State indicators also capture the fact that population sizes differ greatly across districts, which in part explains differences in campaign spending across states (Gierzynski and Breaux 1991, Hogan 2000), and differences in campaign technology. Lastly,?i controls for omitted time invariant state characteristics that simultaneously determine vote shares and the campaign finance regulations.
Redistricting occurred for the 1982, 1992 and 2002 elections. This analysis captures increases or decreases in competitiveness due to state-wide redistricting via state and year effects. This is certainly less than perfect, but aspects of redistricting that are not captured by these effects will only bias the estimated coefficient on contribution limits if redistricting is correlated with the passage of more restrictive campaign finance laws. No theoretical or empirical work suggests that redistricting is correlated with more restrictive campaign finance laws (see, for example, Basehart and Comer (1991) and Heterington, Larson, and Globetti (2003)
Better minds than mine can weigh in, but I think the correlation that would be an issue could be either a correlation of low state limits and "restrained" gerrymandering (hypothesize the good-government state of your choice), or one between wild-west gerrymandering and states that don't impose anything under a $2000 contribution limit. I would just observe that Stratmann is pretty upfront about this issue. He doesn't maintain that his controls eliminate this issue.
Remember the significant finding in the study is between the $2000 plus contribution group, and the $500 and under group. That's it.
