Mean vs Median vs Mode

The mean is the arithmetic average, the median is the middle value when data are ordered, and the mode is the most frequent value. For roughly symmetric data they are similar; for skewed data or outliers, the median is often a better summary of a typical value.

Definitions and use

Illustrative example with worked numbers

Invented for teaching. Length of stay (days) for seven patients: 2, 3, 3, 4, 5, 6, 40. The mean is 63/7 = 9 days, but six of seven patients stayed 6 days or less. The median is 4 days, which describes a typical patient better. The mode is 3 days. The single long stay (40 days) pulls the mean upward.

Choosing and reporting

• Report mean with standard deviation when data are approximately symmetric.
• Report median with interquartile range (or range) when data are skewed or ordinal.
• Look at a histogram or box plot rather than guessing.
• State clearly which statistic you report.

Practical tips

Costs, length of stay, hospital waiting times and many laboratory values are typically right-skewed. Some analyses use transformations (such as logs) and report geometric means; ask a statistician if unsure. Never calculate a mean of an ordinal scale without considering whether it is meaningful.

Common pitfalls

• Reporting a mean without checking for outliers.
• Reporting a mode for continuous data with no repeated values.
• Forgetting to state the number of observations.

Key takeaways

• Choose by the shape of the data.
• Median for skewed data; mean for symmetric.

This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.