In terms of how this is done, the Big 5 personality theory is like a squirrel in the movie, Up. The powerful tool is testing how individual level data predicts

In terms of how this is done, the Big 5 personality theory is like a squirrel in the movie, Up. The powerful tool is testing how individual level data predicts the incremental impact on behavior of actions (ads etc.) that the campaign promoters can take. The behavior you care about ultimately is voting, and you can't train models on voting, but you can train models on campaign donations, Facebook liking, sharing, and copying-and-pasting. These are behaviors that are likely to correlate with voting later. The role of a theory like Big 5 is to help guide the selection of what to test, and is ideally balanced with what is easy to test.