Statistical Error
A survey is all the more accurate as the number of people surveyed is great. The same applies to physics: part of the error on a quantity stems from the fact that the measurement was done a finite number of times. This is the statistical error. Mathematically, it can be shown that the statistical error decreases as the inverse of the square root of the number of measurements. In other words, a 2(10)-time better precision requires 4(100) times more experiments repeated identically.