# pwr.confIntR

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.

- Keywords
- htest

##### 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.

##### See Also

##### Examples

```
pwr.confIntR(c(.4, .6, .8), w=c(.1, .2));
```

*Documentation reproduced from package userfriendlyscience, version 0.6-1, License: GPL (>= 2)*