Expert Predictions of the Outcome in King vs. Burwell

The week before King v. Burwell was announced, I confidentially polled an elite group of health policy and legal experts to get their personally-assessed prior probability that the King plaintiffs challenging ACA subsidies would actually win this case. The somewhat-arbitrary group included leading health economists, political scientists, journalists covering the case. It also included several legal antagonists who had written briefs on the various sides.

I received more than forty responses. Not surprisingly, given my own liberal views, about three-quarters of the responses were from Democrats. Although Democrats and Republicans had wildly different views of who should win, the distribution of predicted probabilities of a plaintiff victory was surprisingly similar between the two groups. Amazingly, Cato’s Michael Cannon and I offered identical prior predictions—20% probability of plaintiff victory.

Among Democrats, the median predicted probability of plaintiff victory was 40%. Among Republicans, the median was 37.5%. The means showed a bit more of a difference between the two groups: 46% among Republicans, 37.5% among Democrats. Yet five of the six highest predicted probabilities of a plaintiff victory came from Democratic experts; two were 70% or higher.
The overall distribution is shown below.

clunky expert poll results

Judging by my admittedly- clunky informal poll, the Obama administration’s emphatic victory surprised many close observers on both sides. Many Democrats reported that the plaintiffs had more than 0.5 probability of winning. Otherwise, why would the Supreme Court have jumped to take the case? We may never know the answer to that question.

We don’t merely know this from polls. Hospital Corporation of America stock rose 8% at the decision’s announcement. (See below from That is an amazing jump, which reflects hospitals’ strong stake in ACA’s effective national implementation.

HCA stock price (

Many states went to considerable trouble devising contingency plans, suggesting that they, too, took this case very seriously indeed.

After the ruling was announced, I tweeted that conservatives magnified their political and legal losses by tethering themselves to a preposterous legal case. I stand by that deep, 140-character argument. Yet it is definitely an ex post argument. The smart money believed that the plaintiffs might well have won.

We’re likely to see a huge amount of hindsight bias applied to this case. From the plaintiff’s perspective, this seems ex post like a more doomed tactical gambit than it actually was, when properly viewed from an ex ante perspective. From my opposing perspective, this is sobering. Fortunately, the same insights make the government’s emphatic victory appear more exhilarating and important than it would otherwise seem to be.

[Cross-posted at The Reality-Based Community]

Harold Pollack

Harold Pollack is the Helen Ross Professor at the School of Social Service Administration at the University of Chicago.