1. Frequency Polygon

2. Frequency Polygon
A frequency polygon is a line graph in which points are joined by straight lines and closed to make a polygon
A frequency Polygon indicates the spread and skewness of distribution.

3. Drawing Frequency Polygon
A frequency polygon is drawn by plotting the frequency (or frequency density) against the midpoints of the data.
It can be superimposed on a histogram by connecting consecutive midpoints of the tops of columns
The area under the polygon represents the frequency of the data ( and is the same as the area of all the bars in the histogram)

4. Example 1

5. Example 1

6. Example 1

7. Example 2

8. Example 2

9. Drawing Frequency Polygon
More Examples for you to try:

10. Analyzing Frequency Polygon
When the sample is large and there is a large number of intervals, since there are a large number of line segments the frequency polygon approaches FREQUENCY CURVE.
The Frequency Curve (or the Polygon) indicates the spread/dispersion of the distribution.
Low Dispersion
High Dispersion

11. Analyzing Frequency Polygon
A Frequency Curve (or the Polygon) also indicates the SKEWNESS (“lopsidedness”) of the distribution.
Normal Curve (symmetric)
Examples
Weight, Height, IQ Test scores

12. Analyzing Frequency Polygon
A Frequency Curve (or the Polygon) also indicates the SKEWNESS (“lopsidedness”) of the distribution.
Positively Skewed Distribution
Examples
Number of children in a family
Age at which women marry
Distribution of wages in a firm
Positive side stretched

13. Analyzing Frequency Polygon
A Frequency Curve (or the Polygon) also indicates the SKEWNESS (“lopsidedness”) of the distribution.
Negatively Skewed Distribution
Examples
Daily maximum temperatures for a month in summer
Reaction times for a experiment
Negative side stretched