National EMSC Data Analysis Resource Center
A "sum" is the sum of all the data (the observations) in a dataset. Once again, we’re using very simple math here. Just add up all the numbers below from a dataset of childhood weights (you can use a calculator if you prefer).
13 36 98 77 42 50
110 22 49 81 26 38
Sum = 13+36+98+77+42+50+110+22+49+81+26+38
The answer is 642. Should this number mean anything to you right now? Not really. It’s good to have, but it will only become useful later on when you use it in other statistical analyses.