Roll-Off, Straight Ticket Voting, and African Americans

So I have now finished playing with my data, and have decided I can put myself out there and place some confidence in the following findings. First, I've got a couple of definitions for reference:

AATOcomp – proportion of turnout in a county which is registered as African American

STVrate – proportion of ballots from a county which used the straight-ticket voting option

Roll-off – proportion of decreased cast ballots in a particular race as compared to the Presidential contest

I've distilled my thoughts into five key observations. These will form the basis of the paper that I'm working on with Professor Aldrich. Please feel free to respond with any thoughts in the comments section. These are just the data findings - what I feel like the numbers tell me - not publishable research. I'm working on developing a political theoretical framework on how they all make sense together. I don't expect to come up with a single unifying theory, but I am going to try to make as much sense of it all as I can.

Overall

1. There is a significant positive correlation between AATOcomp and STVrate. This causes issues in examining the effect of AATOcomp on roll-off due to the necessary relationship between STVrate and roll-off.

On Partisan Races

2. Without controlling for STVrate, higher levels of AATOcomp are associated with higher amounts of roll-off in top ticket races but this effect reverses as we go down the ticket and there is more overall roll-off. The effect is significant but weak at the top of the ticket, but becomes much stronger down the ballot (presumably as a result of a higher proportion of the remaining votes coming from STV). 

3. By subtracting STV vote totals from the overall totals, we can examine roll-off among non-STV ballots.* Using this method, we find that the same positive association between AATOcomp and roll-off exists still in the upper ticket. Continuing to control for STVrate, as we progress down the ticket, we see that there becomes no association at all between AATOcomp and roll-off – with one exception. After the judicial contests, there is the Soil and Water Conservation District Supervisor. In this race there is a very strong positive exponential effect between AATOcomp and roll-off (controlled for STV).

On Judicial Races

4. Surprisingly, there is only a weak positive correlation between judicial roll-off and STVrate. All correlations are positive with bivariate regression slope frequentist p-values < .15 but all are > .01 Controlling for the effects of multiple tests, it is difficult to assert this as a strong effect.

5. In the judicial races, there is no correlation between AATOcomp and roll-off. This makes sense when considered in conjunction with the facts that (1) STVrate has a minimal effect on roll-off in the nonpartisan races (see Observation 4) and that (2) this is a continuation of the trend controlled for STVrate as identified in Observation 3.

*It is important to remember here that we can only study the behavior in the aggregate. We can use this method to understand the voting behavior of the county, but not individuals.