Definition: A histogram is a bar graph for numerical data that groups values into equal-width intervals and shows how many data values fall into each interval.
What is a histogram?
A histogram groups numerical data into intervals called bins and draws one bar per bin. The bar’s height shows the frequency, or count.
How is it different from a bar graph?
Bars in a histogram touch, because the intervals are continuous and ordered along a number line. A bar graph compares separate categories and leaves gaps.
How do you make one?
Take the ages of 15 visitors at a robot expo: 8, 9, 11, 12, 12, 13, 14, 15, 15, 16, 18, 21, 24, 27, 33. Use bins of width 10.
- 0 to 9: 2 values
- 10 to 19: 10 values
- 20 to 29: 2 values
- 30 to 39: 1 value
The tallest bar, 10 to 19, shows where most visitors fall.
What can you see?
The shape: symmetric, skewed right with a long tail, or clustered. This one is skewed right.
What is a common mistake?
Uneven bin widths. Every interval must cover the same span, and each value must belong to exactly one bin.