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Sampling: Single mean

Command:    

 Sampling
Next selectSingle mean

Description

Calculates the required sample size for the comparison of a sample mean with a given value. 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.
  • Mean: the hypothesized mean (considered to be biologically significant different from the null hypothesis value).
  • Standard deviation: hypothesized standard deviation (known from previous studies or from the literature).
  • Null hypothesis value: the null hypothesis value.

Example

In the example the null hypothesis value is 50, and you consider a value of at least 60 to be significant different. From a previous study, you expect the standard deviation of the sample to be 14. 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 21 in this example.

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

Comparison of two paired samples

To calculate the sample size required for the comparison of two paired samples, you use the same procedure as for a Single mean.

In the dialog box, for Mean, you enter the hypothesized mean difference; for Standard deviation, enter the hypothesized standard deviation of the differences, and for Null hypothesis value enter the value 0.

Literature

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

See also