Polls & Margins of Error

How big a sample?

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• A random sample can describe a huge population. The population size barely matters.
• Margin of error is about $\pm 1/\sqrt{n}$. To halve it, quadruple the sample.
• Bias beats size: a large non-random sample can be badly wrong.

Steps

1. Asking a few
2. Margin of error
3. Sample of 400
4. A bigger poll
5. Plus or minus one percent
6. The famous flop