Correlation and influential observations
One observation can change the story a single number tells.
The point that changes the correlation
Seven synthetic observations follow an upward trend. Move an eighth observation up or down to see how the sample Pearson correlation changes. Both axes use arbitrary units.
Pearson correlation (r)—
Last x value8
Last y value8
Show the observations as an accessible table
| Observation | X | Y |
|---|---|---|
| 1 | 1 | 1.0 |
| 2 | 2 | 2.0 |
| 3 | 3 | 2.9 |
| 4 | 4 | 4.1 |
| 5 | 5 | 5.2 |
| 6 | 6 | 5.7 |
| 7 | 7 | 7.3 |
| 8 (moving) | 8 | 8.0 |
An influential observation should prompt investigation, not automatic deletion. Correlation alone cannot establish causation.