Margin of error

The margin of error is an estimate of a poll's variance in reported percentages if the same poll were taken multiple times. The larger the margin of error, the less confidence one has that the poll's reported percentages are close to the "true" percentages, that is the percentages in the whole population.

Related Topics:
Poll's - Population

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The margin of error can be calculated directly from the sample size (the number of poll respondents) and is commonly reported at one of three different levels of confidence. The 99 percent level is the most conservative, the 95 percent level is the most widespread, and the 90 percent level is rarely used. For example, if the level of confidence is 99 percent, there is a probability of at least 99 percent that the "true" percentage in the entire population is within one margin of error of a poll's reported percentage. Equivalently, the margin of error is a lower bound on the radius of the 99 percent confidence interval.

Related Topics:
Confidence

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Note that the margin of error only takes into account sampling error. It does not take into account other potential sources of error such as bias in the questions, bias due to excluding groups who could not be contacted, people refusing to respond or lying (selection bias), or miscounts and miscalculations.

Related Topics:
Sampling error - Selection bias

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