Rae, Gordon (2008) A note on using alpha and stratified alpha to estimate the reliability of a test composed of item parcels. BRITISH JOURNAL OF MATHEMATICAL & STATISTICAL PSYCHOLOGY, 61 (Part 2). pp. 515-525. [Journal article]
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Several authors have suggested that prior to conducting a confirmatory factor analysis it may be useful to group items into a smaller number of item `parcels' or `testlets'. The present paper mathematically shows that coefficient alpha based on these parcel scores will only exceed alpha based on the entire set of items if W, the ratio of the average covariance of items between parcels to the average covariance of items within parcels, is greater than unity. If W is less than unity, however, and errors of measurement are uncorrelated, then stratified alpha will be a better lower bound to the reliability of a measure than the other two coefficients. Stratified alpha are also equal to the true reliability of a test when items within parcels are essentially tau-equivalent if one assumes that errors of measurement are not correlated.
|Item Type:||Journal article|
|Faculties and Schools:||Faculty of Life and Health Sciences|
Faculty of Life and Health Sciences > School of Psychology
|Research Institutes and Groups:||Psychology Research Institute|
Psychology Research Institute > Health and Wellbeing
|Deposited By:||Mrs Fiona Harkin|
|Deposited On:||23 Dec 2009 10:16|
|Last Modified:||24 Feb 2014 10:44|
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