Frequency Polygon

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.

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)

Example 1

Example 1

Example 1

Example 2

Example 2

Drawing Frequency Polygon More Examples for you to try:

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

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

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

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