Sample size or precision for Cronbach's alpha

prec_cronb returns the sample size or the precision for the given Cronbach's alpha.

Usage

prec_cronb(k, calpha, n = NULL, conf.level = 0.95, conf.width = NULL)

Arguments

k

number of measurements/items.

calpha

desired Cronbach's alpha.

n

sample size.

conf.level

confidence level.

conf.width

precision (the full width of the confidence interval).

Value

Object of class "presize", a list of arguments (including the computed one) augmented with method and note elements.

Details

Exactly one of the parameters n or conf.width must be passed as NULL, and that parameter is determined from the other.

Sample size or precision is calculated according to the formula & code and provided in Bonett and Wright (2014).

n is rounded up to the next whole number using ceiling.

References

Bonett, D. G. and Wright, T. A. (2015) Cronbach's alpha reliability: Interval estimation, hypothesis testing, and sample size planning J. Organiz. Behav., 36, pages 3– 15. doi:10.1002/job.1960 . # k= number of items

Examples

# calculate confidence interval width...
prec_cronb (k=5,calpha=0.7,n= 349,conf.level= 0.95, conf.width= NULL)
#> 
#>      precision for Cronbach's alpha 
#> 
#>   calpha k   n conf.width conf.level       lwr       upr
#> 1    0.7 5 349 0.09999076       0.95 0.6467151 0.7467059
# calculate N required for a given confidence interval width...
prec_cronb (k=5,calpha=0.7,n= NULL,conf.level= 0.95, conf.width= 0.1)
#> 
#>      sample size for Cronbach's alpha 
#> 
#>   calpha k   n conf.width conf.level       lwr       upr
#> 1    0.7 5 349        0.1       0.95 0.6466332 0.7467688