Histogram is a pictorial representation method of grouped statistical data. ‘Grouped’ implies the clustering of data with similar attributes or values into ‘classes’. The advantage of such a representation is its pictorial appeal wherefrom one can assess the nature of behaviour of a variable and is hence useful in predicting the probabilistic distribution of this variable.
Say we consider a class of 20 students as our data set. We want to represent the distribution of marks obtained out of 100 by them in the last annual examination as given by a histogram.
We construct a grouped table as on the extreme left with, say, 5 classes or groups of marks, each of width 20 and count the number of students in each class. Then we plot a graph of the same as besides, called the histogram. Along the x-axis, marks are plotted while the number of students is along the y-axis. The width of each bar is the width of the class while the height represents the number of students in the class.