Definition
Histogram
A histogram groups numerical values into intervals and uses touching bars to show how many fall in each interval.
View exact chart data
| Start | End | Frequency |
|---|---|---|
| 0 | 10 | 3 |
| 10 | 20 | 4 |
| 20 | 30 | 2 |
What it means
The bottom of each bar owns a stretch of numbers, such as 0 to under 10. Neighbouring intervals share a boundary, so their bars touch. With equal-width groups, compare heights. If widths differ, compare areas instead.
Remember it
Each histogram bar owns a stretch of the number line, not a category name.
Example
Journey times 3, 7, 8, 12, 13, 16, 18, 21, and 27 minutes give frequencies 3, 4, and 2 in the intervals 0–<10, 10–<20, and 20–<30. Draw three touching equal-width bars with those heights.
Watch for
A chart with separate bars for cats, dogs, and birds compares named groups. Closing the gaps would not change those labels into number intervals.
Common mix-up
Touching bars are a clue, not the whole rule. The horizontal axis must be made of numerical intervals.
Exact meaning
A histogram groups numerical observations into adjoining intervals and draws a rectangle over each interval. Rectangle area represents frequency; when every interval has the same width, height represents frequency too.