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 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