## Section 1.3 Summary

A numerical summary of a distribution should report its **center** and its **spread** or **variability**.

The mean and the median *M* describe the center of a distribution in different ways. The mean is the arithmetic average of the observations, and the median is their midpoint.

When you use the median to describe the center of a distribution, describe its spread by giving the **quartiles**. The **first quartile Q**_{1} has one-fourth of the observations below it, and the **third quartile Q**_{3} has three-fourths of the observations below it.