Seasonality in prediction markets: @Polymarket (blue) has had more volume than @Kalshi (green) on almost every day except Sundays and Mondays because of—you guessed it—sports. Biggest games are on Sundays & Mondays, hence this pattern. Most of Kalshi's sports volume comes through their Robinhood integration which started earlier this year. Recently Polymarket has been picking up more sports volume. But merely looking at weekly volume numbers/market share hides the more obvious pattern. Always look at your data!