Sample size calculation: Correlation coefficient

Command:

Sample size Correlation coefficient

Description

Calculates the required sample size for a correlation coefficient. The sample size takes into account the required significance level and power of the test (see Sample size calculation: Introduction).

Required input

• Type I error - alpha: the probability of making a Type I error (α-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 (β-level), i.e. the probability of accepting the null hypothesis when in fact it is false.
• Correlation coefficient: the hypothesized or anticipated correlation coefficient.

Example

For example, the correlation coefficient between two variables is thought to be 0.60. How many patients are required for this correlation coefficient to be significantly different from 0.0?

For α-level you select 0.05 and for β-level you select 0.20 (power is 80%).

After you click Calculate the program displays the required sample size (19 in the example, meaning that you will need 19 cases in which both variables must be measured).

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

Literature

• Bland M (2000) An introduction to medical statistics, 3^rd ed. Oxford: Oxford University Press.

See also

• Sample size menu
• Sample size calculation: Introduction
• Correlation coefficient

Recommended book

An Introduction to Medical Statistics
Martin Bland

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This textbook is intended for medical researchers and includes the design of clinical trials and epidemiological studies, data collection, summarizing and presenting data, probability, standard error, confidence intervals and significance tests, techniques of data analysis including multifactorial methods and the choice of statistical method, problems of medical measurement and diagnosis, vital statistics, and calculation of sample size.