"Average" is ambiguous. Most often it means the mean, but the median is also an average — and for some data it's the more honest one. Knowing when to use each will keep you from being misled (or misleading others).
What they are
- Mean: add up all the values and divide by how many there are. The everyday "average".
- Median: sort the values and take the middle one (or the average of the two middle ones if there's an even count).
How to calculate each
Take the numbers 2, 4, 9. The mean is (2 + 4 + 9) ÷ 3 = 5. The median is the middle value when sorted, which is 4. For an even set like 2, 4, 6, 8, the median is the average of the two middle values: (4 + 6) ÷ 2 = 5.
When the mean misleads
The mean is sensitive to outliers — a single extreme value drags it up or down. Compare 1, 2, 3, 4 with 1, 2, 3, 100. The medians are similar (2.5 in both), but the means are 2.5 and 26.5. The mean of the second set tells you almost nothing about a typical value.
| Data | Mean | Median |
|---|---|---|
| 1, 2, 3, 4 | 2.5 | 2.5 |
| 1, 2, 3, 100 | 26.5 | 2.5 |
Real-world examples
This is why incomes, house prices, and net worth are usually reported as medians. A few billionaires pull the mean income far above what a typical person earns, while the median — the person in the exact middle — stays representative. When you see "average" attached to skewed money data, check whether it's the mean or the median.
What about the mode?
The mode is the value that appears most often. It's most useful for categories or repeated values — the most common shoe size, say — rather than for summarizing a spread of numbers. For most everyday "average" questions, mean and median are the two you'll reach for.