OK so I don't think I've got it right in the first place.
I've got the participation by counting the number of deals done and then dividing that by 12 and multiplying by 100 to get the participation %. However I noticed that it then splits up the values so all the 1's are on 1 row, all the 2's on the next and so on when I add the participation calculation.
How do I group these together so it's a 1 if there's a value in that month, 0 if it's blank. Count those and then divide by 12 and multiple by 100?