A histogram represents a continuous frequency distribution with touching bars; a bar diagram represents discrete or categorical data with separate bars of equal width.
Histogram
- Used for grouped continuous data such as marks, heights, or salaries in class intervals.
- Class intervals on the x-axis, frequency on the y-axis.
- Bars are adjacent (no gaps) because the classes are continuous.
- The area of each bar represents frequency; with unequal class widths, height = frequency density.
- Shows the shape of the distribution, and the mode can be found graphically.
Example: heights of students: 150–155 cm: 4, 155–160: 10, 160–165: 15, 165–170: 6. Four touching bars, tallest over 160–165.
Bar diagram
- Used for categorical or discrete data, e.g. number of students in each branch, or production in different years.
- Bars of equal width with equal gaps between them; only the height (length) matters.
- Can be vertical or horizontal.
- Types: simple bar diagram, multiple (grouped) bar diagram (e.g. boys and girls side by side for each year), subdivided (stacked) bar diagram, and percentage bar diagram.
Example: students in branches: Computer 120, IT 90, AI&DS 60, Mechanical 45 — four separate bars of these heights.
Differences
| Histogram | Bar diagram |
|---|---|
| Continuous, grouped data | Discrete or categorical data |
| No gaps between bars | Gaps between bars |
| Area shows frequency | Height shows value |
| Widths may differ (class width) | All widths equal |
| Order of classes is fixed | Bars can be reordered |