Histograms

This is a type of non-cumulative frequency graph drawn on a natural scale in which the respective frequencies of the different classes of values are represented through vertical rectangles drawn closed to each other. This type of graph is appropriate for continuous series, although, they might be drawn for discrete series as well. With the help of this graph we can easily determine the value of Mode, a measure of central tendency.

Technique of drawal

1. Represent the class intervals of the variable along the X-axis, and their frequencies along Y-axis on natural scale.
2. Start the Y-axis with zero and the X-axis with either zero, or the lower limit of the lowest class interval. When the lower limit of the series happens to be a minus figure, it should be properly shown on the X-axis to the left of the point, zero.
3. Draw the rectangular bars in vertical manner above each of the class intervals. In doing so, fix the width of each such bar according to the magnitude of the respective class interval shown on the X-axis. Further, fix the length of each such bar in proportion to the frequency as under:

Length of a bar = (Frequency of the class/Magnitude of the class) × standard magnitude of the series

or L =F₁/i₁ × i(s)