Statistics - Organizing and Interpreting Data

Histogram and Frequency Polygon

By graphing a frequency distribution table, the overall distribution of data can be easily observed at a glance.

The following table shows a frequency distribution of weekly TV viewing hours surveyed at Jimin’s school. This data is represented graphically in the following steps.

Weekly Time Spent Watching TV

Steps to Create a Histogram

  1. Mark the endpoints of each class interval on the horizontal axis.
  2. Mark the frequencies on the vertical axis.
  3. For each class interval, draw a rectangle with its width corresponding to the class interval and height corresponding to the frequency.
A graph created using this method is called a histogram.

Steps to Create a Frequency Polygon

  1. In the histogram, mark a point at the center of the top of each rectangle.
  2. Assume there are class intervals with a frequency of 0 at both ends of the histogram, and mark points at their centers.
  3. Connect the marked points with line segments.
A graph created using this method is called a frequency polygon.

Comparing Histogram and Frequency Polygon

Both the histogram and frequency polygon visually represent the distribution of data. However, a frequency polygon is especially useful for comparing the distributions of two or more datasets, making it more convenient than a histogram for such purposes.