Last week Politico leaked a draft majority opinion in Dobbs v. Jackson Women’s Health Organization. PredictIt’s existing market for the Dobbs case had already been predicting the Court would side with the State of Mississippi, and unsurprisingly, moved another 9 cents upon news of the draft opinion.
As of May 8th, three prediction markets – Polymarket, PredictIt, and Smarkets – overwhelmingly predict the U.S. Supreme Court will either strike down Roe v. Wade or uphold Mississippi’s 15-ban on abortion, although they each define their market differently:
| Market | Event Rules | Yes | No |
| PredictIt | “striking down Mississippi’s ban”* | 0.96 | 0.05 |
| Polymarket | “Alito deliver the final majority opinion” | 0.88 | 0.12 |
| Smarkets | “overruling the Roe v Wade” or “upholding Mississippi’s ban” | 0.96 | 0.05 |
*I switched the Yes and No prices for PredictIt to be consistent with the outcomes in the other two markets.
However, the prediction markets seem to be more confident in the Supreme Court upholding the Mississippi ban than whether Associate Justice Samuel Alito is the one to deliver the final majority opinion. The Supreme Court’s traditional secrecy makes it unclear whether Chief Justice John Roberts or a senior justice (most likely Associate Justice Clarence Thomas) assigned the opinion to Alito, and unless more information leaks, we won’t even know when the final decision will be released.
Polymarket’s rules aren’t concerned about the content of the final majority opinion, just that Alito is the author. In the extremely unlikely event that Alito issued a majority opinion that struck down the Mississippi ban and upheld Roe, Polymarket’s Dobbs market would still resolve to “Yes.”
Prediction market traders buy and sell binary option contracts: an event either happens or does not happen (Yes or No). A correct prediction receives $1/share, and a wrong prediction receives $0/share. The market prices can indicate what traders believe is the probability of the event happening.
PredictIt is a prediction market run by Victoria University of Wellington, New Zealand, and Aristotle International, Inc. PredictIt limits both investment amounts and the number of investors per market. Participation is limited to individuals 18 years of age or older who are U.S. Persons.
Polymarket is a decentralized prediction market built on the Polygon blockchain. Traders buy and sell using a stable coin pinned to the U.S. dollar. Trading is not available to people in the United States.
Smarkets is a British online betting exchange, that allows peer-to-peer wagers on sports and politics.