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In several journal articles I read, autors report split-half reliability (Guttman formula obtained if questionnaire is splited into two parts: odd items and even items, usually) together with Cronbach's alpha.

Correct me, please, if I'm wrong: if we calculate split-half reliability for every possible split and take arithmetic mean, we get Cronbach's alpha. So reporting split-half reliability for one single split is pointless, since we report mean for every possible split.

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  • $\begingroup$ Which journal articles? Please provide references for at least a few of them. $\endgroup$
    – Will
    Mar 21 '20 at 21:38
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Indeed, Cronbach alpha is equivalent to the average of all possible split-half estimates, hence it's not really necessary to report both indices, unless odd items and even items (or any other item splits) play a specific role. For instance, sometimes we assess the same item content but using two different wording, or a reverse scoring scheme, to check that subjects are not answering at random, or the polarity of the response options (e.g., 1 = strongly disagree ... 5 = strongly agree versus 1 = strongly agree ... 5 = strongly disagree) does not affect the average responses. Such scenario are really parallel form of the same questionnaire, for which split-half reliability makes sense.

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