Accuracy proportional to size

I have lists of data I'm trying to organize where the list with the least variation/most precision/closest to the average and most amount of data is most highly rated. Some of the lists are like 2000 numbers long and others only have 1 number. Obviously the arithmetic mean of a list with one number will be exactly the value of the one number. Any individual value from a list of 2000 numbers might not be as close to the arithmetic mean. When sorting these, all the smaller lists will be higher rated. It seems really easy, but I can't come up with a way to order the list more proportionally.