Does item homogeneity indicate internal consistency or item redundancy in psychometric scales?

Gregory J. Boyle

Research output: Chapter in Book/Report/Conference proceedingChapterResearchpeer-review


Internal consistency or item homogeneity is often used for estimating intra-scale reliability, in terms of the item variances and covariances derived from a single occasion of measurement. While it is desirable that items in a psychometric scale measure something in common (i.e. exhibit unidimensionality), Hattie (1985) has indicated that there is still no satisfactory index. As Hattie (pp. 157-158) pointed out, a unidimensional scale (having an underlying latent trait), is not necessarily reliable, internally consistent or homogeneous. Hattie concluded that the frequent use of Cronbach's alpha coefficient as a measure of unidimensionality is not justified. Hattie further stated that,

'alpha can be high even if there is no general factor, since (1) it is influenced by the number of items and parallel repetitions of items, (2) it increases as the number of factors pertaining to each item increases, and (3) it decreases moderately as the item communalities increase.'

The subsequent assertion by Ray (1988) that internal consistency of a psychometric scale should be maximised, represents a further restatement of classical itemetric theory, and ignores the previous work of Hattie (1985), and many others, as outlined below. There is an optimal range of internal consistency/item homogeneity, if significant item redundancy is to be avoided (Boyle, 1983, 1985, 1986).

Original languageEnglish
Title of host publicationPsychological Assessment
EditorsG. Boyle, D.H. Saklofske, G. Matthews
Place of PublicationLondon
PublisherSAGE Publications Ltd
Number of pages7
ISBN (Print)9780857022707
Publication statusPublished - 2012


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  • Psychological assessment: Four volume set

    Boyle, G. J., Saklofske, D. H. & Matthews, G., 2012, Los Angeles: SAGE Publications Ltd. (SAGE benchmarks in psychology)

    Research output: Book/ReportScholarly editionResearchpeer-review

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