Technical Appendix: Party and Incumbent Favorability in Senate Elections

These are the regressions which underpin the results presented in this posting.  The dependent variable is the Democratic share of the two-party vote for Senate in each state.  The favorability figure comes from Morning Consult; the Trump approval measure for 2018 comes from Gallup.

  • big chunk of favorability’s effect is partisanship; controlling for Trump support brings the favorability coefficient down
  • no measurable difference in effect of Trump support measured either using his 2016 vote or his 2018 approval
  • two elections had large residuals, Alaska in 2016 where there was a strong third-party contender, and Utah in 2016 where Mike Lee trounced a transgender female Democrat in the home of the Mormons.