[Rasch] Differences in alpha for Winsteps and R

Mike Linacre mike at winsteps.com
Thu Jul 13 08:40:51 AEST 2017


When computing Alpha with missing data, Winsteps does no listwise, 
casewise or other deletion. It does the Cronbach Alpha computation (= 
computes variances) using whatever data are present.

Mike L.

On 7/13/2017 3:08 AM, Stuart Luppescu wrote:
>> The answer is "(approximate due to missing data)" !!
>> >
>> >Cronbach Alpha is defined for complete data, so when data are
>> >missing,
>> >assumptions must be made about those data. Winsteps computes Alpha
>> >as
>> >though the data are complete, and ignores the fact there are missing
>> >data, except for adding the "approximate" message.
> Ah, I see. So, Mike, how does Winsteps compute Alpha "as though the
> data are complete"? I believe that psych::alpha() does listwise
> deletion. Sometimes if there is too much missing data it fails
> completely.

Mike Linacre, mike at winsteps.com or winsteps1234 at gmail.com
Winsteps: www.winsteps.com/winsteps.htm - current version 4.0.0 - June 2017
Facets: www.winsteps.com/facets.htm - current version 3.80.0 - March 2017
Winsteps and Facets Tutorial PDFs at www.winsteps.com/tutorials.htm
Rasch Forum: http://raschforum.boards.net
Your comments and questions are welcomed.
Sydney, Australia, Winsteps Workshop, August 10, 2017.

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