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Stadler, Matthias ORCID: 0000-0001-8241-8723; Sailer, Michael ORCID: 0000-0001-6831-5429; Fischer, Frank ORCID: 0000-0003-0253-659X (January 2021): Knowledge as a formative construct. A good alpha is not always better. In: New Ideas in Psychology, Vol. 60, 100832 [Forthcoming]
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Measurements of domain knowledge very often use and report Cronbach's alpha or similar indicators of internal consistency for test construction. In this short article, we argue that this approach is often at odds with the theoretical conception of knowledge underlying the measure. While domain knowledge is usually described as a formative construct (formed by the manifest observations) theoretically, the use of Cronbach's alpha to construct and evaluate an empirical measure implies a reflective model (the construct reflects in manifest behaviors). After illustrating the difference between reflective and formative models, we illustrate how this mismatch between theoretical conception and empirical operationalization can have substantial implications for the assessment and modeling of domain knowledge. Specifically, the construct may be operationalized too narrowly or even be misinterpreted by applying criteria for item selection that focus on homogeneity such as Cronbach's alpha. Rather than maximizing items internal consistency, researchers constructing measures of domain knowledge should, therefore, make strong arguments for the theoretical merit of their items even if they are not correlated to each other.