# Chapter Summary

### Chapter 4

The mode, the median, and the mean are measures of central tendency—numbers that describe what is average or typical about the distribution.

The mode is the category or score with the largest frequency (or percentage) in the distribution. It is often used to describe the most commonly occurring category of a nomi­nal level variable.

The median is a measure of central tendency that represents the exact mid­dle of the distribution. It is calculated for variables measured on at least an ordinal level of measurement.

The mean is typically used to describe central tendency in interval-ratio variables, such as income, age, or education. We obtain the mean by summing all the scores and dividing by the total (N) number of scores.

In a symmetrical distribution, the fre­quencies at the right and left tails of the distri­bution are identical. In skewed distributions, there are either a few extremely high (positive skew) or a few extremely low (negative skew) values.