Reliability, Dimensionality, and Internal Consistency as Defined by Cronbach: Distinct Albeit Related Concepts

Ernest C Davenport, Mark L Davison, Pey Yan Liou, Quintin U. Love

Research output: Contribution to journalArticlepeer-review

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This article uses definitions provided by Cronbach in his seminal paper for coefficient α to show the concepts of reliability, dimensionality, and internal consistency are distinct but interrelated. The article begins with a critique of the definition of reliability and then explores mathematical properties of Cronbach's α. Internal consistency and dimensionality are then discussed as defined by Cronbach. Next, functional relationships are given that relate reliability, internal consistency, and dimensionality. The article ends with a demonstration of the utility of these concepts as defined. It is recommended that reliability, internal consistency, and dimensionality each be quantified with separate indices, but that their interrelatedness be recognized. High levels of unidimensionality and internal consistency are not necessary for reliability as measured by α nor, more importantly, for interpretability of test scores.

Original languageEnglish (US)
Pages (from-to)4-9
Number of pages6
JournalEducational Measurement: Issues and Practice
Issue number4
StatePublished - Dec 1 2015


  • Cronbach's alpha
  • Dimensionality
  • Internal consistency
  • Reliability

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