Using some form of regressional analysis may be the way to determine the importance of various factors, but what a task without a substantial database. Surely this has already been done for the common factors and the results should be somewhere for us to find.

I just use the simplistic approach of finding the average strike rate of each of the top 5 ranks of each factor and compare the averages to decide what factors to use. With just 2 factors for the past 25 weeks I have managed a pot that fluctuates between 10 and 12%. Not fantastic but has allowed for an enjoyable time punting.

To combine the factors I use a basic probability formula to obtain a rating. The formula is:

Rating (prob of at least one factor getting a winner) =
1 - (1 - prob of factor 1)(1-prob of factor 2)(1-prob of factor 3).........etc
and multiply the result by 100.

Hope this provides something to think about for those without large a database.
Gunny72