The volume of activity on Polymarket, one of the most popular prediction markets, has been significantly inflated by so-called wash trading in which users rapidly buy and sell the same contracts, according to a new study by Columbia University researchers.

The “artificial trading,” as the authors call it, varied over time but accounted for an average of 25% of all buying and selling on Polymarket over the past three years, the researchers concluded.

The paper, which has not undergone peer review, was posted Thursday on the open-access research platform SSRN. A representative for Polymarket said the company didn’t have an immediate comment and was reviewing the study.

The authors do not suggest that Polymarket itself was responsible for the wash trading, but they point to elements of

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