Cronbach alpha — MRCPsych Paper A MCQ

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ModerateEpidemiology and research methodsCronbach alphaMRCPsych Paper A

A 12-item Likert-response anxiety questionnaire is administered once to 300 patients. The investigators want a single coefficient based on the covariation among item scores to estimate how consistently the items function together as one scale. Which statistic is most appropriate?

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Correct answer: B — Cronbach alpha

Cronbach alpha is the best answer because it estimates the internal consistency of a multi-item scale from the covariation among its item scores. The questionnaire was administered once, and the investigators are interested in whether its items function consistently together. An intraclass correlation coefficient is more commonly used for reproducibility of continuous measurements, such as test–retest or inter-rater reliability. Cohen kappa assesses agreement for categorical ratings. Spearman correlation measures the monotonic association between two variables rather than providing an overall internal-consistency coefficient for 12 items. A positive likelihood ratio evaluates diagnostic-test performance. Cronbach alpha does not, by itself, prove that a scale is unidimensional; factor analysis would be required to examine its dimensional structure.

Reference: Ofqual. Measurement Invariance of the Key Stage 2 National Curriculum Science Sampling Test in England, section 4.2: Relationship between subtests and test internal consistency reliability. 2014. https://assets.publishing.service.gov.uk/media/5a82cf4340f0b62305b94769/2014-02-11-measurement-invariance-of-the-ks-2-national-curriculum-science-sampling-test-in-england.pdf