ACDC: 96% of live congressional prediction markets move 5 cents for $3,500 or less

The Anti-Corruption Data Collective (ACDC) said in findings published on 2 November that in 96% of US congressional prediction markets with live order books, a five-cent price shift would cost $3,500 or less. The research raises questions about whether Kalshi's new transparency measures give the public enough information about the money behind election odds, Gambling Insider reported.

According to the report, $431 million had been wagered on congressional markets ahead of the midterm elections.

What happened

ACDC examined 28,845 congressional markets spread over Kalshi, Polymarket and Polymarket US. Betting volumes have nearly tripled compared with the 2024 congressional elections, and there are 61 times as many markets, ACDC said.

Key figures from the research:

• For 66% of live congressional markets, a five-cent move would cost less than $100, while 244 would need more than $10,000.
• Looking at the most expensive market in each of 470 congressional races, 90% could have their price shifted by five cents at a cost under $25,000.
• Volumes under $10,000 were recorded in 90% of markets across the three platforms. Kalshi uses that level as its marker for markets where thin trading can make prices less reliable. ACDC put that six percentage points higher than in September.

ACDC Research Fellow Michelle Kendler-Kretsch told Gambling Insider that Kalshi's October tools, which include low-volume warnings and forecasting-accuracy measures, may help newcomers. She said the tools do not let researchers see which accounts place big orders or measure the sway of individual traders. On Polymarket, she said, transactions can be followed through publicly visible wallets, which is not possible on Kalshi. Gambling Insider said Kalshi had not responded to a request for comment at the time of publication.

ACDC found that on Polymarket, the top 1% of wallets generate 75% of congressional trading volume, compared with 68% in August. It also identified 591 round-trip transactions across 22 markets involving 544 wallets, in which $618,395 changed hands for a combined profit of $34. ACDC said it has not established wash trading or money laundering.

ACDC stressed that its calculations show the cost of moving a price, not whether anyone has tried to rig an election. It also reported $25.5 million wagered on contracts tied to campaign outcomes that insiders could know in advance, such as endorsements.

Industry figures quoted by Gambling Insider offered differing readings. Ben Head, who is COO at BetGoodwin, a bookmaker licensed in the UK, said the $3,500 figure mainly shows how little money is in most markets. Matt Cepulis, CEO of 3betmedia, said cheap price moves can be turned into screenshots that circulate widely.

ACDC also pointed to its work with CNBC on trading on Kalshi around the Los Angeles mayoral primary. It said some influencers who questioned the result had partnership deals with Kalshi, though it was unable to determine if the trading showed genuine enthusiasm or an attempt to keep odds elevated.

Why it matters

Operators and affiliates that publish or promote prediction-market odds may want to check how they present them, since Kendler-Kretsch said the concern is what happens when thin-market prices are passed around as evidence that a candidate is winning. Affiliates with commercial ties to prediction-market platforms could face scrutiny over how those relationships are disclosed when odds are shared in election coverage.

The findings are likely to add to pressure on platforms that do not publish trader-level data. Operators and suppliers working with Kalshi will want to monitor whether it responds on data access, as researchers' ability to audit trading is the central point in the dispute.

The campaign-finance questions are unresolved. Kendler-Kretsch said legal experts consulted by ACDC suggested that trades directed by a campaign could potentially qualify as in-kind contributions, while independent betting would not automatically do so. Compliance teams could need to consider coordination and intent when reviewing such activity.

What's next

ACDC plans to return, after the votes are counted, to markets where prices appeared to conflict with polling or other available information. It aims to identify the trades responsible and to check if specific accounts repeatedly moved prices in the wrong direction.