Five Prediction Markets, Five Definitions of Price: The Normalization Problem Nobody Talks About
Pull the current price for the same event from two prediction market APIs and diff them. Check "Fed cuts rates in September" on Kalshi and Polymarket at the same moment: Kalshi shows YES at 61¢, Polymarket shows YES at $0.58. Three cents isn't rounding error, and it isn't one venue lagging the other. They won't match, and it's not a bug in either API. It's because "price" doesn't mean the same thing on the two platforms you just queried.
That sounds like a minor unit-conversion detail. It isn't. If you're building anything that touches more than one prediction market, a dashboard, a bot, a research tool, a Discord alert, the normalization layer is the actual engineering problem. Get it wrong and a comparison dashboard shows a spread that isn't real, a bot trades on a gap that evaporates once you account for fees, or a research pull quietly treats two...
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