# Crunch that Cali

More network vacuity: CNN feed reading (I paraphrase): "California Democratic Primary competitive between Obama and Clinton. McCain and Romney competing for lead in California." Thank you, Dr. Insight. But what about Huckabee? I thought he was sweeping the massive California rural evangelical vote?

So we're watching California, the last of the punditary puzzles. But Ian Ayres, whose book Super Crunchers I am now reading and highly recommend, thinks he knows what's going to happen:

It turns out that it is really easy to use the raw information of the poll (the leader percent, the follower percent, and the size of the poll) to calculate the probability of leading in the population. In winner-take-all elections (which are not the case for many of the primaries), this “probability of leading” is crucially what we should care about –- because if people don’t change their minds (and, if undecided, break evenly), this is the probability that the poll leader will win the election. But most people have a very hard time making the calculation in their head.

So take a shot: what do you think is the probability that Romney is leading McCain in the population of likely Republican California voters?

Turns out that Romney’s probability of leading is a whopping 92.7 percent. If you want to calculate your own leader probability, I’ve created a simple Excel spreadsheet where you can plug in the numbers and generate an answer for any poll you want.

The same poll found that Barack Obama led Hillary Clinton in California “by 45 percent to 41 percent, with a margin of error of 2.9 percentage points.” The same analysis suggests that, at the time of the poll, there is a 94.2 percent chance that more probable Democratic voters support Obama than Clinton.

Of course, these probabilities may end up being widely off –- either because the poll was poorly done, or because people change their minds. But another advantage of calculating the probable leader statistic is that it builds a better bridge to the prediction markets. Just after the poll was announced, Intrade had Romney’s probability of winning in California as 94 percent (pretty close to the 92.7 percent leader probability). But Obama’s InTrade bond for California was only trading at 59.9 percent — substantially below his leader probability of 94.2 percent.

I think we have to take seriously the possibility of systematic bias. These models use estimates of likely voters based on the last round of elections, but anecdotal evidence suggests that turnout is a little different from the normal pattern.