A frequency polygon is a line graph that represents the shapes of the statistical distributions. To draw the graph, simply construct a histogram, and join the middle top points of the bars of the histogram with a line. You need a pencil, a ruler and a piece of paper.
- Draw a histogram
Using the data in question, formulate the class intervals. Construct a table showing the class intervals and the corresponding values of the frequencies. The table makes it easy for you to draw the histogram. Use a pencil and a ruler to draw the Cartesian plane. Let the x-axis represent the class intervals, whereas the y-axis shows the frequencies of the class intervals. Plot the values of the frequencies against the class intervals. Draw the bars of the histogram to represent this data.
- Calculate the values of the midpoints
Find the value of the midpoint of each class interval. The midpoint of each class is calculated by getting the sum of the class boundaries and then dividing it by two.
- Draw the frequency polygon
Using the midpoint values, mark the middle of each bar at the top with a pencil. Join the points with line segments. Ensure that the lines on the two ends of the graph touch the x-axis of the plane in order to demonstrate the continuity of the data values.