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 volume is sports (>80%), coming 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!