prec_cronb
returns the sample size or the precision for the given
Cronbach's alpha.
prec_cronb(k, calpha, n = NULL, conf.level = 0.95, conf.width = NULL)
number of measurements/items.
desired Cronbach's alpha.
sample size.
confidence level.
precision (the full width of the confidence interval).
Object of class "presize", a list of arguments (including the computed one) augmented with method and note elements.
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
.
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
# 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 n conf.width conf.level lwr upr
#> 1 0.7 349 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 n conf.width conf.level lwr upr
#> 1 0.7 349 0.1 0.95 0.6466332 0.7467688