Proportion Margin of Error

Understand the proportion margin of error result

Proportion Margin of Error is designed for checking reported polling precision or planning how sample size changes uncertainty. It asks for sample proportion, sample size, critical z value and reports margin of error. The standard error of a proportion is multiplied by the selected normal critical value. The decimal result can be multiplied by one hundred to read it as percentage points. By exposing margin of error, Proportion Margin of Error makes this specific arithmetic inspectable instead of presenting an unexplained number.

With the page defaults of Sample proportion 0.5, Sample size 100, Critical z value 1.96, the verified output is Margin of error 0.098. Margin of error does not include bias from wording, coverage, or nonresponse. In Proportion Margin of Error, each labeled default remains visible while you edit, so you can change one assumption at a time and trace how margin of error responds.

Method, limits, and private processing

This normal approximation is not reliable for every small or highly imbalanced sample. Proportion Margin of Error evaluates the entered values entirely in your browser, without sending the inputs to a server. When using its margin of error, retain the stated method and input units because this result is bounded by the assumptions of the standard error of a proportion is multiplied by the selected normal critical value.