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Sampling: Single proportion

Command:    

 Sampling
Next selectSingle proportion

Description

Calculates the required sample size for the comparison of a proportion with a given proportion. The sample size takes into account the required significance level and power of the test (see Sampling: Introduction).

Required input

  • Type I error - alpha: the probability of making a Type I error (Alpha-level, two-sided), i.e. the probability of rejecting the null hypothesis when in fact it is true.
  • Type II error - beta: the probability of making a Type II error (Beta-level), i.e. the probability of accepting the null hypothesis when in fact it is false.
  • Proportion (%): the hypothesized proportion (considered to be biologically significant different from the null hypothesis value), expressed as a percentage.
  • Null hypothesis value (%): the null hypothesis value (a proportion, expressed as a percentage).

Example

In the example the null hypothesis value is 50%, and you consider a proportion of at least 70 to be significant different. For Alpha-level you select 0.05 and for Beta-level you select 0.10.

After you click the Calculate button, or press the Enter key, the program will display the required sample size, which is 62.

A table shows the required sample size for different Type I and Type II Error levels.

Literature

  • Kirkwood BR, Sterne JAC (2003) Essential medical statistics, 2nd ed. Oxford: Blackwell Scientific.

See also