Confidence interval

A confidence interval gives a range for an unknown population parameter instead of a single guess, acknowledging that samples vary. Its width reflects the uncertainty in the estimate: more data and less spread give a narrower interval. For example, a 95% confidence interval of 52% plus or minus 3% for support runs from 49% to 55%. The general form is $\text{estimate} \pm (\text{critical value}) \times (\text{standard error})$, where the standard error measures the typical size of sampling error.