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userfriendlyscience (version 0.7.2)

# pwr.confIntR: Determine required sample size for a given confidence interval width for Pearson's r

## Description

This function computes how many participants you need if you want to achieve a confidence interval of a given width. This is useful when you do a study and you are interested in how strongly two variables are associated.

## Usage

`pwr.confIntR(r, w = 0.1, conf.level = 0.95)`

## Arguments

r

The correlation you expect to find (confidence intervals for a given level of confidence get narrower as the correlation coefficient increases).

w

The required half-width (or margin of error) of the confidence interval.

conf.level

The level of confidence.

## Value

The required sample size, or a vector or matrix of sample sizes if multiple correlation coefficients or required (half-)widths were supplied. The row and column names specify the `r` and `w` values to which the sample size in each cell corresponds. The confidence level is set as attribute to the resulting vector or matrix.

## References

Bonett, D. G., Wright, T. A. (2000). Sample size requirements for estimating Pearson, Kendall and Spearman correlations. Psychometrika, 65, 23-28.

Bonett, D. G. (2014). CIcorr.R and sizeCIcorr.R http://people.ucsc.edu/~dgbonett/psyc181.html

Moinester, M., & Gottfried, R. (2014). Sample size estimation for correlations with pre-specified confidence interval. The Quantitative Methods of Psychology, 10(2), 124-130. http://www.tqmp.org/RegularArticles/vol10-2/p124/p124.pdf

Peters, G. J. Y. & Crutzen, R. (forthcoming) An easy and foolproof method for establishing how effective an intervention or behavior change method is: required sample size for accurate parameter estimation in health psychology.

`pwr.confIntR`
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