A reporter asked me the other day why political scientists are so sure that people vote based on the economy. I told him there are three big pieces of evidence:

1. Comparing elections. As Doug Hibbs and others have shown, there’s a strong correlation between the incumbent party’s share of the vote and economic conditions in the year preceding the election.

2. Comparing voters within an election. As Ansolabehere, Rodden, and Snyder, and others have shown, individuals’ views of the national economy are a good predictor of their votes.

3. Voters’ stated concerns. When asked what are the most important issues, voters lead with “job creation/economic growth” (23%) and “energy/gas prices” (20%), with, in total, 59% of voters identifying economic issues as most important, as compared to 16% mentioning Iraq, 8% mentioning terrorism, 8% immigration, and 5% environment. The economy isn’t the only issue, but it’s central.

If there’s a factor that predicts elections, individual votes, and it’s what people say that it matters to them–then we’re inclined to believe them.