Note 8 — Chapter III · ToC

There are two methods of stating the representative value of a group, the average and the median. Everyone knows the average. The median is obtained by arranging the values in linear series from the smallest to the greatest and taking the middle one. When should one use the average, and when the median? It is not easy to give a general rule, but in this case of spelling, we have a good example. If we wish to calculate the number of mistakes for each age, to take the average might be a disastrous proceeding. A single child who made a hundred or so mistakes would obviously make the average unfairly high. The median is affected much less by such aberrant cases, and consequently is more suitable for very heterogeneous series, in which the difference between the maximum and the minimum is very great.