US Congress has truly prodigious re-election rate: 80-90% in the House since 1964, and ~80% in the Senate with exception of 1970s (when it hit a "low" of 55%-65%)
While there are a lot of different factors contributing to this incumbent advantage, it is frequently stated that gerrymandering [1] contributes significantly to it.
Is there any sort of data/research available which quantifies just how much of an impact does gerrymandering have on re-election rates compared to other factors?
I'm fine if the data is specific to US Congress (slightly preferred), or US in general, or some other locale.
NOTES:
[1] Gerrymandering is defined on Wikipedia as "a practice that attempts to establish a political advantage for a particular party or group by manipulating geographic boundaries to create partisan or incumbent-protected districts".
In plain terms, you adjust the district so that (in terms of reelections) the incumbent has a higher percentage of his partisans in the new district than in the old one, and higher than percentage of opponents. This makes the district safer for the incumbent and increases the chances of winning re-election.
