# [R] Correlations Table of Items when compute Cronbach's Alpha

David L Carlson dcarlson at tamu.edu
Tue Feb 21 18:44:15 CET 2017

```Actually you will need ?psych::alpha to get the help page. The correlations provided in output\$item.stats are with the total score. If you want a correlation matrix for the original 4 variables you can use sweep() to invert the necessary column(s):

> cor(sweep(dat, 2, c(1, 1, 1, -1), FUN="*"), use="complete.obs")
X1        X2        X3        X4
X1 1.0000000 0.1396653 0.1916540 0.2865590
X2 0.1396653 1.0000000 0.5184912 0.2938423
X3 0.1916540 0.5184912 1.0000000 0.5037861
X4 0.2865590 0.2938423 0.5037861 1.0000000

If you use check.keys=TRUE you can extract the vector from the results:

> output <- alpha(dat, check.keys=TRUE)
Warning message:
In alpha(dat, check.keys = TRUE) :
Some items were negatively correlated with total scale and were automatically reversed.
This is indicated by a negative sign for the variable name.
> output\$keys
[1]  1  1  1 -1

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Mark Sharp
Sent: Tuesday, February 21, 2017 11:14 AM
To: Steven Stoline <sstoline at gmail.com>
Cc: r-help at r-project.org
Subject: Re: [R] Correlations Table of Items when compute Cronbach's Alpha

Have you looked at the help page?
?alpha::alpha

See the section labeled Value.

Look at
output <- alpha(data, keys = c(1, 1, 1, -1))
output\$r
output\$r.cor
output\$r.drop

R. Mark Sharp, Ph.D.
msharp at TxBiomed.org

> On Feb 21, 2017, at 9:43 AM, Steven Stoline <sstoline at gmail.com> wrote:
>
> Dear All:
>
>
> I am using *alpha(data, **check.keys=TRUE)  or  alpha(data, keys = c(1, 1,
> 1, -1))*  to compute the Cronbach's Alpha. I am using  *check.keys=TRUE*
> or *keys = c(1, 1, 1, -1) *to automatically reverse items.
>
>
> *My question is: *how can I get the correlation tables (matrix) of the
> reversed items as part of the R output.
>
>
>
> *Here is an example of the data set:*
>
>
> X1 X2 X3 X4
>  2  5   4   4
>  1  1   1   6
>  1  2   1   6
>  2  3   2   4
>  1  2   1   6
>  1  3   1   6
>  2  2   2   5
>  2  1   1   6
>  2  2   4   5
>  5  5   2   1
>  1  3   1   6
>  1  1   1   6
>  1  1   1   6
>  2  2   2   5
>  2  2   2   2
>  1  6   1   6
>  1  2   1   6
>  2  2   3   5
>  2  5   4   5
>  2  1   2   6
>  2  2   1   5
>  2  2   2   6
>  1  1   1   6
>  1  1   1   6
>  1  1   1   5
>  1  2   2   5
>  2  2   2   5
>  1  2   2   5
>  1  4   2   5
>  2  2   2   2
>  2  2   4   5
>  2  1   2   5
>  2  2   2   5
>  2  2   2   5
>  2  2   2   5
>  2  2   2   5
>  5  2   2   5
>  2  2   1   5
>  2  5   6   2
>  2  4   2   5
>  2  2   2   4
>  2  3   5   1
>  3  3   3   6
>  2  2   2   4
>  2  2   2   5
>  2  2   2   5
>  1  1   1   6
>  1  1   1   5
>  6  1   1   6
>  1  1   1   6
>  2  6   4   3
>  1  1   1   6
>  1  1   1   6
>  4  5   5   5
>  5  2   2   5
>  2  2   2   5
>  1  2   1   6
>  1  5   1   6
>  1  4   2   5
>  2  1   1   5
>  4  2   1   5
>  2  2   2   5
>  1  1   1   6
>  6  1   1   4
>  1  2   1   6
>  1  1   1   5
>  1  1   1   6
>  1  4   1   3
>  1  1   1   6
>  5  2   2   5
>  2  2   2   5
>  1  1   1   6
>  1  1   1   5
>  4  4   2   4
>  3  2   2   5
>  1  2   1   6
>  1  2   1   6
>  2  1   1   5
>  2  6   1   6
>  4  3   1   5
>  1  1   1   5
>  1  1   1   6
>  4  5   4   5
>  1  1   1   2
>  1  1   1   6
>  1  1   1   6
>  4  4   3   4
>  2  2   2   4
>  1  2   2   4
>  1  1   1   6
>  2  3   2   5
>  2  6  NA   5
>  2  2   2   5
>  1  2   3   4
>  2  1   2   5
>  1  2   2   6
>  1  1   2   6
>  1  2   2   5
>  2  2   2   5
>  1  5   5   2
>  1  2   1   5
>  1  5   2   4
>  2  4   1   6
>  6  1   1   2
>  2  2   2   5
>  1  1   1   6
>  1  1   1   2
>  2  2   2   4
>  1  1   1   6
>  4  2   2   5
>  2  3   1   5
>  2  1   2   5
>  2  2   1   5
>  1  2   2   5
>  1  2   1   5
>  6  2   2   4
>  2  2   5   2
>  2  5   3   5
>  1  4   4   4
>  1  1   1   6
>
>
> thank you
> steve
>
> ------------------------
> Steven M. Stoline
> sstoline at gmail.com
>
> [[alternative HTML version deleted]]
>
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