Execution-quality concept
Polymarket slippage explained
Slippage is the difference between the best visible price and the effective average price you get after your selected size consumes available orderbook levels.
Why slippage happens
A market may show a best ask at 42¢, but that does not mean every entry size can fill at 42¢. If only a small amount is available at that level, a larger entry may consume higher asks at 43¢, 44¢, or beyond.
The result is an effective entry price that is worse than the visible price. That difference is execution friction.
Simple orderbook example
If 20 dollars can fill near the best ask but 200 dollars must consume several levels, both entries may be looking at the same market while facing very different execution quality.
RealityGap treats the selected size as part of the analysis because slippage is size-sensitive.
What slippage does not tell you
Low slippage does not mean the market is a good prediction. High slippage does not mean an outcome is wrong. Slippage only describes execution quality, not probability accuracy.
Related concepts
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