Which statistic expresses the uncertainty around a survey’s estimate?

• A. The sample size
• B. The p-value
• C. The margin of error
• D. The confidence interval

Answer: (C)

Uncertainty around a survey estimate is quantified by the margin of error. This statistic tells you how far the sample result could plausibly differ from the true value in the population due to sampling variation. For example, if the estimate is 60% with a margin of error of ±3 percentage points, the true population value is likely between 57% and 63% at the chosen confidence level. The margin of error depends on sample size and how variable the data are: larger samples produce smaller margins, giving a more precise estimate. The margin of error is closely connected to the confidence interval, since the interval is the range formed by taking the estimate and adding and subtracting the margin of error. The p-value measures something different—the probability of observing your data under a null hypothesis and does not express uncertainty about the survey estimate.