You Make the Market

How it works

1. You see some dice face-up and quote a bid (price you'll buy at) and an ask (price you'll sell at) on the total
2. An informed trader sees all the dice and trades whenever the true sum is outside your quote: you lose the distance
3. If the true sum is inside, you earn a fair-market bonus that shrinks as your spread widens, and turns negative if the spread is far wider than the uncertainty
4. Your score rates how close each quote's expected value is to the best possible quote, so luck does not count. The result shows the best quote

Exact payoff: inside your quote you earn σ − 0.35 × (ask − bid); outside, you lose how far the true sum is past your quote. σ is the standard deviation of the hidden dice's sum (about 1.71 × √hidden dice without events).

Too tight gets picked off; too wide pays for the width. The best quote is usually about 2 standard deviations of the hidden sum wide.