The arithmetic mean adds the values and divides by their count. The median identifies the middle of the ordered values, using the average of the two central values when the count is even.
A very large or small value can move the mean considerably while leaving the median less affected. That does not make one summary universally better. The choice depends on the question and the distribution being described.
Look at the underlying values or a useful distribution view alongside either summary. Include the count and any relevant grouping. A single measure can be convenient, but the shape of the collection often explains why two reasonable summaries tell different stories.
- Identify which summary is being reported.
- Look for unusually large or small values.
- Keep the distribution and count in view.
A small working example.
A group of ordinary task durations and one unusually long task can make different summaries tell different stories. Inspect the values behind either summary.
A note to keep beside it.
Keep the question beside the number. A measure is easier to interpret when the reader knows which decision or comparison it was intended to support.
Follow a related question
Identify the behavior being tested.
What an environment is forCompare one object under two light sources.
A color depends on the lightKeep learning
Related background to continue exploring this subject.
NIST: statistical engineering NIST: the International System of Units