http://www.ck12.org Chapter 1. Introduction to Physical Science
1.31 Descriptive Statistics
- State why descriptive statistics are useful.
- Identify the mean, median, and mode of a sample.
- Describe the range of a sample.
The girls in this picture vary in height. The shortest girl has a height of 52 cm, and the tallest girl has a height of
64 cm. The other two girls fall in between these two extremes. How could you describe the heights of all four girls
with a single number? How could express how they vary in height with another number?
Using Statistics to Describe a Sample
The girls in the picture above make up a small sample—there are only four of them. In scientific investigations,
samples may include hundreds or even thousands of people or other objects of study. Especially when samples are
very large, it’s important to be able to summarize their overall characteristics with a few numbers. That’s where
descriptive statistics come in. Descriptive statistics are measures that show the central tendency, or center, of a
sample or the variation in a sample.
Describing the Center
The central tendency of a sample can be represented by the mean, median, or mode.
- Themeanis the average value. It is calculated by adding the individual measurements and dividing the sum
by the total number of measurements. - The median is the middle value. To find the median, rank all the measurements from smallest to largest and
then find the measurement that is in the middle. - The mode is the most common value. It is the value that occurs most often.