*! version 1.0.0 16Oct2025

Title

alphaplot -- plots Cronbach's alpha for increasing subsets of a variable list

Syntax

alphaplot
varlist
[if] [in]
[,
format(%fmt)
twoopts(twoway_options)
[alpha_options]
]

varlist should be comprised of items in a factor, sorted by loading values from high to low

format(%fmt) display format for the alpha values on the graph; default is format(%6.3f)

twoopts(twoway_options) specify all available options for twoway graphs

[alpha_options] specify all available options for alpha

Description

alphaplot produces a plot of Cronbach's alpha coefficients for increasing subsets of items (k) in the varlist ranging from 2 to k.
The variables specified in varlist should represent the items loaded onto a factor, ordered by their loading values from high to low. alphaplot
is a useful tool to visualize the diminishing returns of reliability with an increasing number of items loaded on a factor. However, alphaplot is not a
substitute for content expertise, and it is possible that a different subset of items may represent the construct better than that based on sequential loading values alone.

Options

format(%fmt) specifies the format for displaying the alpha values on the plot. The default is format(%6.3f).

twoopts(twoway_options) specifies all available options for twoway graphs.

[alpha_options] specifies all available options for alpha.

Examples

Setup

. use "https://www.stata-press.com/data/r19/sp2.dta", clear

we perform factor analysis using the maximum likelihood method and limiting the output to 3 factors

. factor ghp31- ghp05, ml factor(3)

we then rotate the factors and suppress output for values < 0.40. We also normalize the values

. rotate, normal blanks(0.40)

we now use alphaplot to plot the loadings on factor 1 in increasing subsets, starting from 2 up to 9. We specify the loadings
in the varlist in order from high to low

. alphaplot pf02 pf04 pf03 pf05 rkind rkeep pf01 pf06 sact0

same as above but we now specify that the alpha coefficients be standardized

. alphaplot pf02 pf04 pf03 pf05 rkind rkeep pf01 pf06 sact0, std

Stored results

alphaplot stores the following in r():

Scalars

r(N) number of observations

matrices

r(results) a 2 X k matrix of results shown on the plot

Citation of alphaplot

alphaplot is not an official Stata command. It is a free contribution
to the research community, like a paper. Please cite it as such:

Linden A. (2025). ALPHAPLOT: Stata module to plot Cronbach's alpha for increasing subsets of a variable list

Authors

Ariel Linden

President, Linden Consulting Group, LLC

alinden@lindenconsulting.org

Also see

Help: factor, alpha, splithalf (if installed)