Arbitrage speculated that our predictions are scored like a probability. Data scientists give float values as predictions, ranging from 0 to 1, and predictions they're not really sure about end up at .5. He said if you look at the tails, top and bottom, and pretended that was a portfolio of a long and a short, you can kind of see how you would do with regards to performance. "For our actual results," he said, "you take our predictions, put them in a rank from high to low, and then take the actual stocks and see how they did ranked high to low, and compare how similar those are. That's your scoring metric."