Using multilevel modeling of state-level economic data and individual-level exit poll data from the 2000 Mexican presidential election, we find that income has a stronger effect in predicting the vote for the conservative party in poorer states than in richer states—a pattern that has also been found in recent U.S. elections. In addition (and unlike in the U.S.), richer states on average tend to support the conservative party at higher rates than poorer states. Our findings are consistent with the 2006 Mexican election, which showed a profound divide between rich and poor states. Income is an important predictor of the vote both at the individual and the state levels.
Here’s the paper, and here’s the key graph:
The little circles in the plots show the data from the exit poll from the 2000 election (average vote plotted vs. income category within each state, with size of the circles proportional to the number of survey respondents it represents). Party is coded as 1=PRD, 2=PRI, 3=PAN, so higher numbers are more conservative. The solid line in each plot represents the estimated relation between vote choice and income within the state (as fitted from a multilevel model). The gray lines represent uncertainty in the fitted regression lines.
The graph shows the 32 states (including Mexico, D.F.) in increasing order of per-capita GDP. The slopes are higher–that is, income is a stronger predictor of the vote–in poor states. Income is a less important predictor in the rich states (except for the capital, Mexico, D.F., which has its own pattern).
Here’s a plot of the slopes vs. per-capita GDP in the 32 states:
The conservative party did better with rich voters everwhere, but individual income is a much stronger predictor of the vote in poor states than in rich states. This is similar to the pattern we found in the U.S. One difference between the two countries is that in the U.S., the conservative party does better in the poor states, but in Mexico, the conservative party does better in the rich states. But at the level of individual voting, the patterns in the two countries seems similar.
We plan to replicate our study with 2006 exit polls, once we can get our hands on the data.