 # Sample size: Confidence Interval for a difference between paired proportions

 Command: Sample size Confidence Interval estimation & Precision Difference between paired proportions

## Description

Calculates the required minimum sample size for the estimation of a confidence interval with a required width for a difference between paired proportions (Machin et al., 2009).

Note that the calculation does not include a null hypothesis value or a factor for power (1−β). Therefore the estimated sample size does not give a certainty that a particular value will fall inside or outside the confidence interval. The number of cases is only the number required to attain a specified confidence interval width.

## Required input

• Confidence level (%): select the confidence level: 90, 95 or 99%. A 95% confidence level (the value for a 95% Confidence Interval) is the most common selection. You can enter a different confidence level if required.
• Proportion in group 1 (%): the proportion in the first set of observations
• Proportion in group 2 (%): the proportion in the second set of observations
• Correlation coefficient: the correlation between the pairs of observations.
• Confidence interval width (2-sided): this is the required total width of the confidence interval. For example when a difference is 40% with 95% Confidence Interval 35 to 45, then the confidence interval width is 10.

## Example ## Literature

• Machin D, Campbell MJ, Tan SB, Tan SH (2009) Sample size tables for clinical studies. 3rd ed. Chichester: Wiley-Blackwell.