This calculator estimates a plausible range for a population mean or proportion from sample data, mainly for surveys, experiments, and research reports.
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Choose whether you are estimating a mean or proportion, then enter the sample result, sample size, variability information, and confidence level. Use a t critical value for a mean when the population standard deviation is unknown.
The interval is estimate ± margin of error. For a mean, margin of error = critical value × standard error, where standard error = standard deviation / square root of sample size; for a proportion, standard error = square root of [p × (1 - p) / n].
A survey finds that 55% of 1,000 respondents support a proposal. At 95% confidence, the margin of error is about 1.96 × square root of [0.55 × 0.45 / 1,000] = 3.08 percentage points, giving an interval from 51.92% to 58.08%.
Not in the usual frequentist interpretation. It means the method would capture the true value in about 95% of repeated samples.
Increase the sample size, accept a lower confidence level, or reduce measurement variability. Only the first option is usually a respectable fix after data collection starts.
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