I can give you one method: you'll have to find what to call it.
1) take the attendance of the last five years; add all numbers and divide by 5 to give you the average attendance.
Just thought of this:
2) again look at last 5 years; see if you can get a percentage of increase for each year.
Did it increase 5% or more each year? Then take the % from just the previous year (2014) & give that to the 2015 race to project for 2016 race.
