Mean and median
The idea
The mean is the sum divided by the number of observations. The median is the middle value after sorting, or the average of the two middle values for an even count. Outliers can affect the mean more than the median. Choose a summary suited to the question.
Worked example
For 2, 3, 4, 5, and 26, the mean is 8 but the median is 4. The large value raises the mean; neither statistic alone describes the full distribution.
Another application
For 9, 2, 7, 4, sort to 2, 4, 7, 9. The median is (4 + 7) ÷ 2 = 5.5. The mean is 22 ÷ 4 = 5.5 here, but the two summaries need not coincide.
A common misunderstanding
Finding the middle requires sorting first. The middle position in an unsorted list is not necessarily the median.
Try it yourself
Find mean and median for two small datasets. Add one unusually large value and compare how the summaries change.
Check your understanding
What is the median of 1, 3, 8?
Reveal the explained answer
3, the middle value after sorting.