The histogram is the graphical presentation of the continuous frequency distribution drawn by the help of rectangular vertical bars whose heights represent the frequencies of the classes. The width of the bar remains the same if the class interval is equal and the width may vary in case of unequal class intervals. In histograms, the class intervals are measured along the x-axis and frequencies along the y-axis. While constructing a histogram, the following considerations should be made.
- For a histogram, the frequency distribution should be continuous and exclusive.
- Mid-points given: If only the mid-points are given, the distribution must be converted into a continuous one in the exclusive series.
- Discrete frequency distribution: Histogram can be used to present discrete frequency distribution by converting the discrete values into continuous series.
- Open-end classes: In the case of open-end classes, the histogram cannot be constructed. But if a histogram is to be drawn, the class interval is assumed to be the same at the end class interval as in other classes.
- Histogram with unequal classes: In the case of the unequal class of frequency distribution, the class interval must be equal before constructing the histogram.
Example:
| Monthly income (Rs.) | (No. of workers) |
| 100 – 200 | 28 |
| 200 – 300 | 35 |
| 300 – 400 | 45 |
| 400 – 500 | 50 |
| 500 – 600 | 30 |
| 600 – 700 | 27 |
| 700 – 800 | 24 |
Above diagram is the example of Histogram.
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