I have a project which requires me to predict the injury time of a football match.
I have the relevant information, such as goals, corners, referee, 2 team names and the injury time for each half.
I tried to use Poisson regression and I am confused how I can include referee as a factor in my model? As different referees were involved in a different number of matches. Say Tom was involved in 200 games while Jerry was in 30 games.
I tried to add the factor "referee" into the model and the summary told me that only some of the referees have a significant effect on the results. So I wonder is it correct to add the referee into the model directly, and are there any other methods I can use?
Thanks!