Frequency Polygons

What is a Frequency Polygon?

A frequency polygon is a graphical way to represent the distribution of data. It is created by plotting points directly above the midpoints of each class interval at a height corresponding to the frequency of the class, and then connecting these points with straight lines.

Frequency polygons are useful for comparing different data sets and for visualizing the shape of the data distribution.

How to Construct a Frequency Polygon

1. Find the Midpoints: Calculate the midpoint for each class interval. The midpoint is the average of the upper and lower boundaries of the class.
2. Plot the Points: On a graph, plot the points using the midpoints on the x-axis and the frequencies on the y-axis.
3. Connect the Points: Use straight lines to connect the plotted points. Extend the lines to the x-axis at both ends to close the polygon.

Example: Constructing a Frequency Polygon

Consider the following frequency distribution:

Class Interval	Frequency
10 - 20	5
20 - 30	8
30 - 40	12
40 - 50	7
50 - 60	3