Michael Gilbert has posted this draft on SSRN. Here is the abstract:

Scholars debate whether law or politics motivates judges’ decisions. Jurisprudential philosophies and political ideologies correlate, making it difficult to isolate these factors. Using a novel survey technique, I identify the correct legal outcome – under plain language and purposive methods of interpretation – in a large number of cases involving the single subject rule. The rule limits ballot propositions to one “subject,” a malleable standard that may invite ideological decision-making. Direct measures of law correlate strongly with judges’ votes, suggesting that judges behave objectively in these disputes. Controlling for law, measures of ideology also correlate with judges’ votes, suggesting that ideology matters too. The magnitude of the effect of law appears to exceed that of politics. I also find that ideology has the strongest association with judges’ votes when propositions are politically salient, when reviewing judges have extreme political views, and when the law is indeterminate.

I read an earlier version of this piece and recommend it highly. John Matsusaka and I discuss it in our forthcoming Election Law Journal piece on the single subject rule. We’ve also debated Gilbert and Bob Cooter on the rule in relation to their Columbia article on the topic. See also their reply.