Wednesday, November 7, 2018

How NC's 2018 State Legislative Districts "Behaved" in Relationship to Trump's 2016 Vote

In a previous blog post, I noted that there appeared to be a close relationship to how a Republican state legislative candidate performed (that is, the vote percentage that GOP candidate received in the district) compared to the district's vote for Donald Trump in 2016.

Now that we have the preliminary election results and percentages for both state house and state senate Republican candidates, I decided to re-run the analysis to see what, if any, association was present between Trump's vote percentage in the new state legislative districts and the GOP candidate's vote percentage in the 2018 election.

In doing so, I ran a fairly simple 'descriptive' analysis by a scatterplot, where the X (horizontal) axis was Trump's 2016 vote percentage in the 2018 state house and state senate districts, with the Y (vertical) axis being the Republican state legislative candidate's vote percentage. I included a line of 'best fit' between the two; for example, if Trump's 2016 vote percentage in a district was 50 percent and the GOP's candidate was 50 percent, then Trump's percentage would 'explain' the GOP candidate's percentage 100 percent (otherwise known as an adjusted r-squared of 1.0 for a perfect explanation or association between the two factors).

As a reminder, this scatterplot shows Trump's 2016 percentages to the 2016 GOP state senate candidate's percentage in the districts that were drawn for 2016's election:

In this scatterplot, Trump's 2016 vote percentage explains, or correlates, 95 percent of the 2016's GOP state senate candidate's vote percentage in the 2016 version of the district.

For the state house GOP candidates, here's the 2016 scatterplot:

Unlike in the state senate, Trump's 2016 vote percentage explains 82 percent of the 2016's GOP state house candidate's vote percentage in the 2016 version of the district; a little lower, but still a powerful variable used in explaining how the GOP state house candidate's performance would be based on Trump's vote.

What this tells me is that in North Carolina, the 'top of the ticket' (i.e., Trump's vote) is a powerful explainer of, or correlation to, a key 'down ballot' election.

Now, here's the 2018 districts and the recent election performance, with Trump's 2016 vote adjusted to the new 2018 districts (data for which can be found here), first for the North Carolina state senate:

Next, North Carolina's state house:

In terms of both the state house and senate Republican candidates, over 97 percent of their vote percentage in the 2018 districts can be explained by the 2016 vote percentage (adjusted for the new 2018 districts) for Donald Trump.

In statistical terms, 97 percent indicates a powerful correlation between Trump's vote performance in a state legislative district and the GOP candidate's vote performance in that same district. And considering that both chambers saw an increase in the power of correlation between the two factors, it may mean that the North Carolina's partisan loyalty voting has increased in strength. More analysis (and a deeper sense of the various factors in a district) will be important to confirm this hypothesis, and hopefully that will be done in the next few weeks.

As I would think about this preliminary analysis, what we are seeing, potentially, is the strength and power of voting at the presidential level and its influence at the general assembly level, and that presidential party loyalty is strongly associated with state legislative party loyalty. Meaning, it appears that partisanship dominates down the ballot and tribalism through voting is intense.