So the total number is the way we see how close each person was?
Why not summing the differences between each prediction and the actual value?
The way it is right now I could say 9M for PS4, 11M for WiiU and 18.5M for XOne and would be totally accurate...far more than someone saying 18M for PS4, 9.5M for WiiU and 12M for XOne. Does it make sense?
Prediction made in 14/01/2014 for 31/12/2020: PS4: 100M XOne: 70M WiiU: 25M
Prediction made in 01/04/2016 for 31/12/2020: PS4: 100M XOne: 50M WiiU: 18M
Prediction made in 15/04/2017 for 31/12/2020: PS4: 90M XOne: 40M WiiU: 15M Switch: 20M
Prediction made in 24/03/2018 for 31/12/2020: PS4: 110M XOne: 50M WiiU: 14M Switch: 65M