What is the typical salary? What is the IQ score of the average Joe? About how well educated are most American voters? These common types of questions are questions about the center of a distribution of scores. When we ask them, we want a single number that summarizes where most people fall on a given scale. Measures of center answer this question because most people are average. That is, most people fall around the average on any given scale. The more extreme a score is, the less likely it is to occur and the farther away from them mean it is.
We will consider three major measures of central tendency in this text:
These three measures are appropriate for data measured at different levels and are only accurate as measures of center under certain conditions. We will consider each in turn in a later section. For now, we will simply describe them.
The mean is what we usually mean when we talk about an average. The mean is the sum of the scores divided by the number of scores. The median is the middlemost score in a distribution of scores. The median is most often used where there are extreme scores in the distribution that would unduly influence the mean. The mode is the most frequently occurring value in a distribution.
Last Modified: 02/18/2019