3. DEFINITION OF FREQUENCY POLYGON
A frequency polygon is a graph that uses lines that connect
points plotted for the frequencies at the midpoints of the
classes; frequency are represented by the heights of the
midpoints.
OR
Polygon is a form of diagrammatic presentation of data. It is
formed by joining all the mid points of the tops of all rectangles.
However they can be formed even without constructing a
histogram.
4. DRAWING FREQUENCY POLYGON
Frequency polygons can be drawn in two ways;
1. With a Histogram.
2. Without a Histogram.
5. FREQUENCY POLYGON: WITH A
HISTOGRAM
Class limits No. of Sarees
100-200 10
200-300 27
300-400 37
400-500 24
500-600 20
600-700 15
700-800 10
The total area excluded from the
histogram is
Equal to the area included under
frequency polygon.
7. CONSTRUCTION OF FREQUENCY POLYGON
To construct a frequency polygon following steps are imported:
I. Find the midpoints of each class.
II. Draw the X-axis andY-axis.
III. Label the X-axis with the midpoint of each class then use a suitable scale
for the frequencies on theY-axis.
IV. Using the midpoints for the X values and the frequencies as theY values,
plot the points.
V. Connect adjacent points with line segments.
VI. Draw a line back to X-axis at the beginning and end of the graph (where
the next mid points would be located).
8. EXAMPLE OF CONSTRUCTING A
FREQUENCY POLYGON
Test scores Frequency Mid points
49.5---59.5 5 54.5
59.5---69.5 10 64.5
69.5---79.5 30 74.5
79.5---89.5 40 84.5
89.5---99.5 15 94.5