Mean, median & spread
Drag the data. Watch what moves the mean, what the median ignores, and what spread really measures.
guess first, then play →
PredictFirst, a guess
ExploreDrag the data
Drag a dot to move it · tap the line to add a dot · tap a dot to select it.
- Count
- 5
- Mean ▲
- 4
- Median ◆
- 4
- Mode
- none
- Range
- 4
- IQR
- 3
- SD
- 1.41
ConceptsWhat each measure really tells you
Imagine the line is a seesaw and every dot weighs the same. The ▲ is the only place it balances: the total distance on the left equals the total on the right.
Half the dots are on each side of the ◆. Drag the biggest value as far right as you like: the median doesn't move, because the order didn't change.
When a few values stretch out to one side, the mean is pulled toward them and the median stays with the crowd.
The tallest stack. Data can have no mode (nothing repeats), one, or several — and the mode can sit far from the mean and median.
Range uses only the two extremes. The IQR is the spread of the middle half, so it shrugs off outliers. The standard deviation is the typical distance from the mean — every value counts, so outliers inflate it.
Add the same amount to every value: the centre moves, the spread stays exactly the same. Stretch every value away from the mean: the centre stays, the spread grows.
Add a new value exactly equal to the mean: the mean doesn't change, but the standard deviation goes down — the new value adds no distance but one more value to share it.