Is aggregate shot quality significant?
To observe the magnitude of shot quality, I have constructed a shot quality model that estimates the probability of each shot going in, based on the same factors of Krzywickis model plus the game score. This then allowed me to calculate, for the 90 team-seasons of the last 3 years, the expected goal differential based on shot differential and the expected goal differential based on shot quality. Because I am only calculating shot quality differential, arena biases should not have a large impact on my result. Aggregate numbers for my sample were: • An average of 1785 even-strength shots for/against per team • Average shooting percentage per shot of 8.0% with standard deviation of 7% This means that, simply by luck, we would expect the standard deviation of expected goals of a team due to shot quality to be sqrt(1785 * 2) * 7% = 4.2 goals, and we would expect the luckiest of the teams in our sample to have somewhere in the order of +11 goals (almost 3 standard deviations), and the unluck
