Change Check
Did the number really move?
One answer, two polls: say what each poll found and how many people each asked. You get the change and the margin of that change, which is wider than either poll's own margin.
Example (made-up numbers)
95% confidence
- First poll 44.0%±3.4 · 800 asked
- Second poll 48.0%±3.5 · 800 asked
Inside the margin
Up 4.0 points, inside the change's margin of ±4.9.This pair of polls does not show a change. Several polls moving the same way say more than one pair.
- Change
- +4.0
- Margin of the change
- ±4.9
- Each poll's margin
- ±3.4 / ±3.5
Note: sampling error only, treating the two polls as independent samples. Why the change has a wider margin.