Looking at play stats for Dow, Thornton, and Perry's BO2 Zombies Rounds
I will try to qunatify differences in each player and also try to predict the number of kills each player gets based on what round they get to.
I expect that there is a non-linear relationship between rounds and kills because the number of zombies available to be killed increases with the number of rounds. I think that a linear model will still work for the range of rounds between 5 and 25. I expect the linear models to break down before 5 rounds and after 25.