scaleStructure
scaleStructure
The scaleStructure function (which was originally called scaleReliability) computes a number of measures to assess scale reliability and internal consistency.
If you use this function in an academic paper, please cite Peters (2014), where the function is introduced.
Usage
scaleStructure(dat=NULL, items = 'all', digits = 2, ci = TRUE, interval.type="normaltheory", conf.level=.95, silent=FALSE, samples=1000, bootstrapSeed = NULL, omega.psych = TRUE, poly = TRUE)
scaleReliability(dat=NULL, items = 'all', digits = 2, ci = TRUE, interval.type="normaltheory", conf.level=.95, silent=FALSE, samples=1000, bootstrapSeed = NULL, omega.psych = TRUE, poly = TRUE)
Arguments
 dat

A dataframe containing the items in the scale. All variables in this
dataframe will be used if items = 'all'. If
dat
isNULL
, a thegetData
function will be called to show the user a dialog to open a file.  items
 If not 'all', this should be a character vector with the names of the variables in the dataframe that represent items in the scale.
 digits
 Number of digits to use in the presentation of the results.
 ci

Whether to compute confidence intervals as well. If true, the method
specified in
interval.type
is used. When specifying a bootstrapping method, this can take quite a while!  interval.type

Method to use when computing confidence intervals. The list of methods
is explained in
ci.reliability
. Note that when specifying a bootstrapping method, the method will be set tonormaltheory
for computing the confidence intervals for the ordinal estimates, because these are based on the polychoric correlation matrix, and raw data is required for bootstrapping.  conf.level
 The confidence of the confidence intervals.
 silent

If computing confidence intervals, the user is warned that it may take a
while, unless
silent=TRUE
.  samples
 The number of samples to compute for the bootstrapping of the confidence intervals.
 bootstrapSeed
 The seed to use for the bootstrapping  setting this seed makes it possible to replicate the exact same intervals, which is useful for publications.
 omega.psych

Whether to also compute the interval estimate for omega using the
omega
function in thepsych
package. The default point estimate and confidence interval for omega are based on the procedure suggested by Dunn, Baguley & Brunsden (2013) using theMBESS
functionci.reliability
(because it has more options for computing confidence intervals, not always requiring bootstrapping), whereas thepsych
package point estimate was suggested in Revelle & Zinbarg (2008). Thepsych
estimate usually (perhaps always) results in higher estimates for omega.  poly
 Whether to compute ordinal measures (if the items have sufficiently few categories).
Details
This function is basically a wrapper for functions from the psych and MBESS
packages that compute measures of reliability and internal consistency. For
backwards compatibility, in addition to scaleStructure
,
scaleReliability
can also be used to call this function.
Value
 An object with the input and several output variables. Most notably:
References
Dunn, T. J., Baguley, T., & Brunsden, V. (2014). From alpha to omega: A practical solution to the pervasive problem of internal consistency estimation. British Journal of Psychology, 105(3), 399412. doi:10.1111/bjop.12046
Eisinga, R., Grotenhuis, M. Te, & Pelzer, B. (2013). The reliability of a twoitem scale: Pearson, Cronbach, or SpearmanBrown? International Journal of Public Health, 58(4), 63742. doi:10.1007/s0003801204163
Gadermann, A. M., Guhn, M., Zumbo, B. D., & Columbia, B. (2012). Estimating ordinal reliability for Likerttype and ordinal item response data: A conceptual, empirical, and practical guide. Practical Assessment, Research & Evaluation, 17(3), 112.
Peters, G.J. Y. (2014). The alpha and the omega of scale reliability and validity: why and how to abandon Cronbach's alpha and the route towards more comprehensive assessment of scale quality. European Health Psychologist, 16(2), 5669.
Revelle, W., & Zinbarg, R. E. (2009). Coefficients Alpha, Beta, Omega, and the glb: Comments on Sijtsma. Psychometrika, 74(1), 145154. doi:10.1007/s113360089102z
Sijtsma, K. (2009). On the Use, the Misuse, and the Very Limited Usefulness of Cronbach's Alpha. Psychometrika, 74(1), 107120. doi:10.1007/s1133600891010
Zinbarg, R. E., Revelle, W., Yovel, I., & Li, W. (2005). Cronbach's alpha, Revelle's beta and McDonald's omega H: Their relations with each other and two alternative conceptualizations of reliability. Psychometrika, 70(1), 123133. doi:10.1007/s1133600309747
See Also
omega
, alpha
, and ci.reliability
.
Examples
## Not run:
# ### This will prompt the user to select an SPSS file
# scaleStructure();
# ## End(Not run)
### Load data from simulated dataset testRetestSimData (which
### satisfies essential tauequivalence).
data(testRetestSimData);
### Select some items in the first measurement
exampleData < testRetestSimData[2:6];
### Use all items
scaleStructure(dat=exampleData);
### Use a selection of three variables (without confidence
### intervals to save time
scaleStructure(dat=exampleData, items=c('t0_item2', 't0_item3', 't0_item4'),
ci=FALSE);
### Make the items resemble an ordered categorical (ordinal) scale
ordinalExampleData < data.frame(apply(exampleData, 2, cut,
breaks=5, ordered_result=TRUE,
labels=as.character(1:5)));
### Now we also get estimates assuming the ordinal measurement level
scaleStructure(ordinalExampleData, ci=FALSE);