As described in sections 3.2 and 3.3 of the new PDF, the prediction model performed well last week. The median predicted delegates for Trump-Cruz-Kasich were 108-4-6, which compares well to the actual final delegate totals of 111-2-5.

The delegate model converted the actual voting shares in the states to actual delegates almost perfectly (only off by one in Rhode Island), and the model’s 80-percent confidence intervals for voting shares and delegates happened to contain the true value in all cases.

Chapter 4 shows updated model parameters intended to predict going forward. Table 4.2 shows probabilities of winning Indiana: Trump about 90 percent, Cruz about nine percent, and Kasich less than one percent. The vote-share 80-percent confidence intervals for today’s primary and Nebraska’s next week are as follows:

Trump: 41–66 percent (Indiana) and 31–57 percent (Nebraska)

Cruz: 17–41 (Indiana) and 27–55 percent (Nebraska)

Kasich: 10–26 (Indiana) and 8–23 percent (Nebraska)

Adding everything together, Trump’s probability of winning on the first ballot is now 94 percent according to the model (Table 4.5). That looks bleak for Cruz but, if Cruz wins Indiana, Trump’s probability of winning on the first ballot falls immediately to about 70 percent (Table 4.9). Indiana does indeed look rather like “do or die” for Cruz.

If Cruz wins this evening, every future state looks better for him, especially California. For example, the Nebraska 80-percent confidence intervals would become:

Trump: 21–42 percent

Cruz: 44–68 percent

Kasich: 7–21 percent

Under this scenario, the probability of Cruz winning Nebraska and California rises from 48 and 7 percent (respectively) to 95 percent and 22 percent. Overall, the expected net delegate gain for Cruz relative to Trump if Cruz wins Indiana is about 270 delegates. This dynamic is a result of our correlation assumptions.

So provided Cruz wins Indiana, he would still have decent prospects of keeping Trump from 1237.