Monday, September 25, 2017

The owl of Minerva, part 3

In May I had a post about factors associated with support for Donald Trump in the presidential election.  This post elaborates about one of those factors, income.  I used American National Election Studies data to do a series of (binary logistic) regressions on income controlling for various factors.  Here are the estimated effects of income, with a positive sign meaning that higher income goes with a greater chance of voting for Trump:

Controls                  estimate      se
1. none                   .007          .005
2. black, white,
Hispanic, other          -.014          .006

3. plus gender           -.016          .006

4. plus education         .000          .006

5. plus married          -.013          .007

So conclusions about the effect of income depend on what you control for.  If you just compare people with higher incomes to people with lower incomes, it seems those with higher incomes were more likely to vote for Trump.  But if you compare people of the same ethnicity, gender, education, and marital status, it seems those with higher incomes were less likely to vote for Trump.  I think that the second comparison is more meaningful, because we know that ethnicity, education, gender, and marital status made a difference in voting.  However, income doesn't make much difference either way, and is not statistically significant in 1, 4, and 5 (which is why I just say "it seems").  The income variable had 28 categories, and an estimate of -.013 means that going from an income of 25-27,000 (category 8) to 100-109,000 (category 23) would change the probability of supporting Trump vs. Clinton from .5 to .452.
    By comparison, here are the estimates for the other control variables:

White            0.73
Black           -2.32
Hispanic        -.90
Female          -.19
Education      -.15
Married           .63

Education had 16 categories, and the impact of going from a high school graduate with no college (9) and a college graduate (13) was 4*.15=0.6, which is bigger than the impact of going from the lowest to highest income categories (28*.013)=.36.

The basic conclusion is that income was not an important factor in the choice between Trump and Clinton; education was.  This is not surprising, given what is known about the relationship between education and political opinions.  What is surprising for me is that marital status was also an important factor--the difference between married and unmarried people was about the same as the difference between college graduates and people with just a high school diploma.  I knew that marital status was a factor in Democratic vs. Republican support in recent elections, but thought that it was on the same order as gender.

PS:  Data from exit polls shows some increase in support for Trump as income increases.  The difference between the ANES and exit poll data is statistically significant.  My guess is that the ANES estimates are more accurate, partly because the response rate is probably higher, and partly because the exit poll sample is not designed to be representative with respect to anything except which candidate people voted for.  The practical reason I use ANES data is that the individual-level data for the exit polls hasn't been released yet.  But it's safe to say that controlling for the factors discussed here would push the exit poll estimates towards zero.

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