A histogram is a two-dimensional graphical representation of a continuous frequency distribution.
A histogram is a special type of bar diagram.
A histogram is a way of summarizing data pictorially. Histograms show the distribution of the data. They are constructed from a frequency table, which is a summary of the data. The general format for a histogram is a vertical scale that demonstrates frequencies and a horizontal scale that represents the individual intervals, sometimes called classes. Bars are used to represent each individual interval with the height of the bar corresponding to the frequency.
A histogram is drawn according to the steps given below.
- Prepare a grouped frequency distribution table of the given data.
- Show class-limits on X-axis with a suitable scale.
- Show frequencies on Y-axis with a suitable scale.
- Draw rectangles having base equal to the class limits and heights proportional to the frequencies. These rectangles should be joined to each other.
A frequency distribution table is shown below.
The following points can be inferred from the above histogram.
- It is not necessary that the scale on the X-axis and the Y-axis be the same. Different scales may be taken on the axes considering the nature of the data, size of the paper etc. A histogram should look neat and attractive.
- The position of origin on the Y-axis is according to the scale, which is not so on the X-axis. This is indicated by drawing
mark on
- the X-axis near the origin. If necessary, the mark can be made on the Y-axis or on both axes.
- In a histogram, it is necessary that the adjacent rectangles be attached to each other. Therefore, if the given classes are not continuous, it is necessary to make them continuous e.g.; if the classes are 2 to 5, 6 to 9, 10 to 13,…. It should be as 1.5 to 5.5, 5.5 to 9.5, 9.5 to 13.5…
