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I have one question about using SPSS to calculate Cronbach's alpha of a measure that draws on two types of items: one yields ordinal data and the other dichotomous. The ordinal data are produced through 4-point rating items and the dichotomous data through true-and-false questions.

Is it still OK for me to use the reliability analysis option to calculate the Cronbach's alpha for the measure?

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I have tried to edit your question so as to clarify and to eliminate some opportunities for misunderstanding. If I have not kept your original meaning, please rollback my edits. – rolando2 Oct 7 '12 at 0:37

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I've seen instruments like yours evaluated with Cronbach's alpha going back about 50 years. An example is the Marlowe-Crowne Social Desirability Scale, which is based on all dichotomous items. See Psychlopedia.

That Cronbach's alpha can incorporate such types of data is confirmed by SPSS's Help files. Upon clicking Analyze...Scale...Reliability Analysis...Help...Reliability Analysis Data Considerations, I see: "Data can be dichotomous, ordinal, or interval, but they should be coded numerically."

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