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A watchdog group says 88% of the roughly 18,000 active congressional prediction markets could have their prices moved by 10 cents with a single wager under $1,000. The finding, reported by CNBC four days before the midterms, goes to the heart of how far a prediction market price can be trusted.
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Here is what the Anti-Corruption Data Collective found, what the platforms say in reply, what Kalshi has changed, and how to tell a meaningful price from a thin one.
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This article reports what researchers and companies have said. For live odds, see our 2026 midterm elections predictions hub.
What the Watchdog Found
| Finding | Figure |
|---|---|
| Markets that a single wager under $1,000 could move 10 cents | 88% of about 18,000 active congressional markets |
| Big markets with large price spikes | 38 of 167 markets worth more than $100,000, about 23%, had spikes of 30 cents or more |
| Growth since 2024 | Wagers on 2026 congressional contracts have more than tripled those on the 2024 races |
| Who is watching versus trading | Kalshi says viewers outnumber traders 5 to 1 in its midterm markets |
The group, a nonprofit based in Washington, DC, analysed markets across Polymarket International, Polymarket US and Kalshi, according to CNBC.
What a Price Spike Does and Does Not Mean
A 30 cent move in a large market is a big swing. But a spike is not proof that someone manipulated the price. It can reflect real news, a new poll or a rumour that traders believed.
What the findings do show is that many of these markets are small enough for one trade to shift the price, and that even some large markets swing sharply. A reader following a price on a House race with a few thousand dollars traded is looking at a number that one person could change.
What the Platforms Say
- Kalshi: says its election markets are well calibrated, that efforts to manipulate odds are cancelled out by other buyers, and that it has added tools to show readers how much confidence to place in a price.
- Polymarket: rolled out an election-specific surveillance system “to detect potential attempts to manipulate election markets, distort probabilities, or manufacture apparent market consensus.”
What Kalshi Changed
Earlier in October, Kalshi added transparency features to its midterm election markets, according to CNBC:
- Labels for thin markets. Markets with little trading activity are now marked.
- Live feeds of individual trades. Users can see trades as they happen.
Both are designed to help readers judge how much weight to give a price. Look for the label before you quote a number.
Integrity Enforcement So Far
| Action | What was reported |
|---|---|
| Kalshi suspensions | Six 2026 candidates suspended for improperly betting on their own races (CNN) |
| Kalshi staffer blocks | A system using FEC data to block campaign staffers, with “dozens” blocked by July. NPR found one staffer who got around it |
| Polymarket investigations | “Dozens” of election bets investigated, at least two reportedly referred to the CFTC (NPR, citing an unnamed source) |
| The Senate | Newsweek reports the Senate has banned its members and staff from trading on prediction markets |
For more on the investigations, see our report in politics predictions on Polymarket’s election surveillance.
Do the Odds Change Votes?
Some researchers worry about that. Bloomberg’s reporting notes broader concerns that the odds may influence election outcomes, citing a study finding that odds can dissuade voters from believing in a candidate’s electability if they reflect a one-in-three chance of victory.
The platforms say their markets provide useful information and are a complement to polls. Both views are in the evidence, and neither has been settled by the 2026 results yet.
How to Tell a Meaningful Price From a Thin One
- Check the volume. A market with millions traded is far harder to move than one with a few thousand dollars.
- Look for the thin-market label on Kalshi.
- Watch the live feed if there is one. A single large trade is easy to spot.
- Compare with polls and models. A price far from every other source deserves caution.
- Trust the big markets more. Control of the House and Senate carry far more money than any single race.
- Do not read a swing as a verdict. It can reflect news, a rumour or one trade.
Our guide to markets versus polls shows how the major races look side by side.
Election Betting Is Not Legal Everywhere
Roughly two dozen states prohibit betting on elections under existing law, and whether those laws apply to prediction markets is being contested. Most Americans polled by Reuters/Ipsos oppose election betting. Nothing here is a recommendation to trade. See our state-by-state guide.
Frequently Asked Questions
Can prediction markets be manipulated?
A watchdog says most midterm markets are small enough that one bet under $1,000 could move the price by 10 cents. Platforms say manipulation attempts are cancelled out by other traders.
What did the Anti-Corruption Data Collective find?
That 88% of about 18,000 active congressional markets could be moved 10 cents by a bet under $1,000, and that about 23% of large markets had price spikes of 30 cents or more, according to CNBC.
Does a price spike mean someone manipulated the market?
No. A spike can reflect real news. It does mean the price can swing sharply, which is a reason to check volume before trusting a number.
What has Kalshi done about thin markets?
It added labels for markets with little trading and live feeds of individual trades to its midterm markets.
Are the big control markets also easy to move?
They carry far more trading than individual races, which makes them harder to move. The House control market on Kalshi had about $171 million traded as of 1 November, according to one tracker.
Do prediction market odds affect how people vote?
Researchers cited by Bloomberg worry they might. The platforms say the odds provide useful information. The question is not settled.
Prediction markets are not sportsbooks. Event contract trading involves significant risk and is not appropriate for everyone. You can lose your entire stake, and most people who trade on prediction markets lose money. Platforms are typically 18+ and are not available in all states, and some states prohibit betting on elections. This article reports statements by researchers and companies and is not legal, financial or voting advice. GamingToday does not endorse any candidate or party. If gambling or trading stops being fun, call 1-800-GAMBLER for confidential support.
