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Correlations Table of Items when compute Cronbach's Alpha

3 messages · Steven Stoline, Mark Sharp, David L Carlson

Steven Stoline
# 
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
Mark Sharp
# 
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
CONFIDENTIALITY NOTICE: This e-mail and any files and/or...{{dropped:10}}
David L Carlson
# 
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):
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:
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.
[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
CONFIDENTIALITY NOTICE: This e-mail and any files and/or...{{dropped:9}}