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Glossary Math & Statistics

Sample size

Sample size is the number of observations in a study; bigger samples give narrower margins of error.

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In more detail

For a proportion, n = z² × p(1 − p) / e². With 95% confidence (z = 1.96), p = 0.5 and a margin of ±5%, you need 384.16, so 385 responses. The margin shrinks with √n, so halving it needs four times the data.

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See also

  • Glossary Confidence interval
    A confidence interval is a range around a sample estimate that would contain the true value in a stated share (such as 95%) of repeated.
  • Glossary Standard deviation
    Standard deviation measures how far values typically stray from their mean; it is the square root of the variance.
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