# 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.