Cumulative frequency curve or an Ogive curve : The graphical representation of a cumulative frequency distribution is called the cumulative frequency curve or ogive.
There are two methods to construct ogives :
(i) Less than ogive :
In this method, an ogive is cumulated upward. Scale the cumulative frequencies along the y-axis and exact upper limits along the x-axis. The scale along the y-axis should be such as may accommodate the total frequency.
Step I. Form the cumulative frequency table.
Step II. Mark the actual upper class limits along the x-axis.
Step III. Mark the cumulative frequency of the respective classes along the y-axis.
Step IV. Plot the points (upper limits, corresponding cumulative frequency).
By joining these points on the graph by a free hand curve, we get an ogive of 'less than' type.
(ii) More than ogive :
In this method, an ogive is cumulated downward. Scale the cumulative frequencies along the y-axis and the exact lower limits along the x-axis.
Step I. Scale the cumulative frequencies along the y-axis and the actual lower limits along the x-axis.
Step II. Plot the ordered pairs (lower limit, corresponding cumulative frequency). To complete an ogive, we also
plot the ordered pair (upper limit of the highest class,0).
Step III. Join these plotted points by a smooth curve. The curve so obtained is the required 'more than' type ogive.
