We have discussed why it intuitively feels as though lanky Irish beanpole Gareth MacAuley is over-priced to score in this weekend’s match against Big Sam’s Palace.
Analytically, the key building block is the probability of GMac scoring any given WBA goal. Over 26 matches, WBA have scored 36 goals, and GMac has scored 6 of those. That’s a decent sample so let’s start on the basis he’ll score 1 goal in every 6 WBA score.
Using Paddy Power’s correct score market, adjusted for the 125% over-round book, we can compute the probability of WBA scoring 0 goals (26%), 1 goal (35%), 2 goals (23%), 3 goals (11%) etc.
Using GMac’s probability of not scoring (5/6), we can calculate the probability of GMac scoring given a certain WBA scoreline. For example, if WBA score 2, the probability of GMac scoring is 1-(5/6*5/6) = 30%.
Applying the weightings for each WBA scoreline derived from the correct score market to the probability of GMac scoring for each WBA scoreline, we derive the weighted average probability of GMac scoring as 20%.
This suggests the fair odds are 4-1. By quoting 15-2, Paddy Power are suggesting GMac scores approximately 1 in 12 of WBAs goals consistent with previous seasons, and that his strikes this season are statistically anomalous. We’re happy to take that view on.