Frequency Polygon

A graph which is used for understanding the shapes of distributions is known as a frequency Polygon. A Frequency Polygon works as histogram; it is useful for comparing the Sets of data. A graph line is drawn by joining all the mid points of a top of a bar of a histogram. It is also useful for displaying the properties of cumulative distribution. Or we can say that a frequency polygon is a closed figure which is obtained by joining the middle points of the top of rectangles of Histograms. The extreme values are joined with the x-axis at the half distance of class interval from the variable of the class interval.
Now we see how a frequency polygon can be constructed?

For constructed a frequency polygon we have to follow some of the steps which are:
Step 1: First we have to take the middle Point of a class interval on the x-axis.
Step 2: Now we take the frequency on the y- axis.
Step 3: Now we join the points which are obtained by x-axis and y-axis. Two extreme points are joined with the base in such manner that they touch x-axis at half of the distance of the class interval outside the extreme points.

When we design the histogram and frequency polygon then we join the mid points which are situated on the top of the rectangles and the extreme points outside the rectangles.
The relative frequency is related to the class intervals which can be shown with the help of frequency polygon.
It also gives the ideas related to the shapes of the data distribution and in a frequency polygon the two end points always lie on the x- axis or it is a graphical display of a frequency table and the intervals of a frequency polygon are always shown on x-axis.