Histograms
by David M. Lane
Prerequisites
• Chapter 1: Distributions
• Chapter 2: Graphing Qualitative Data
Learning Objectives
- Create a grouped frequency distribution
- Create a histogram based on a grouped frequency distribution
- Determine an appropriate bin width
A histogram is a graphical method for displaying the shape of a distribution. It is particularly useful when there are a large number of observations. We begin with an example consisting of the scores of 642 students on a psychology test. The test consists of 197 items each graded as “correct” or “incorrect.” The students' scores ranged from 46 to 167.
The first step is to create a frequency table. Unfortunately, a simple frequency table would be too big, containing over 100 rows. To simplify the table, we group scores together as shown in Table 1.
Table 1. Grouped Frequency Distribution of Psychology Test Scores
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