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.

`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.

## Author

Douglas Bonett (UC Santa Cruz, United States), with minor edits by
Murray Moinester (Tel Aviv University, Israel) and Gjalt-Jorn Peters (Open
University of the Netherlands, the Netherlands).

Maintainer: Gjalt-Jorn Peters gjalt-jorn@userfriendlyscience.com

## Examples

```
pwr.confIntR(c(.4, .6, .8), w=c(.1, .2));
#> w = 0.1 w = 0.2
#> r = 0.4 273 70
#> r = 0.6 161 43
#> r = 0.8 56 18
#> attr(,"conf.level")
#> [1] 0.95
```