A New View of Statistics Go to: Next · Previous · Contents · Search · Home Summarizing Data: SIMPLE STATISTICS & EFFECT STATISTICS continued
Simple Statistics: THE MIDDLE
A statistic that represents the middle of the data is called a measure of centrality. The best is the mean or average. Just add up all the numbers and divide by the sample size. The mean is the best measure, partly because it uses more information in the data than any other measure of centrality.

The median, or "middle" number, can be useful for data with a non-normal distribution. To work it out, arrange the numbers in rank order (smallest to largest), then count in from one end until you find the middle. (If the sample size is an even number, take the average of the two middle numbers.) The median is not affected by outliers, which is a big point in its favor. But if you're interested in getting an estimate of the center of a population or of a subgroup of a population--and you usually are--the median is a coarse or "noisy" measure.

The mode, or most frequent number, is the only other measure of centrality you'll ever encounter. I've never used it.