Cronbach's α is a measure of what?

• A. Kappa statistic
• B. Split-half reliability
• C. Cronbach's α
• D. Inter-rater reliability

Answer: (C)

Cronbach's alpha measures internal consistency reliability for a set of items that are intended to measure the same underlying construct. It assesses how closely related the items are, reflecting how well they hang together as a scale. As the average correlation among items increases (and as you have more items that relate to the same construct), alpha goes up, indicating stronger internal consistency. Values typically range from 0 to 1, with higher values suggesting better reliability; a common rough benchmark is around .70 or higher, though interpretation depends on context. Remember that alpha assumes the scale is largely unidimensional and that items contribute similarly to the construct; it can be inflated by having many items or by redundant items, and a high alpha doesn’t guarantee that the scale is measuring the intended construct (validity).

The other options don’t fit because the Kappa statistic measures agreement between raters for categorical judgments; split-half reliability is another way to assess internal consistency but Cronbach's alpha generalizes that approach to use all item intercorrelations; and inter-rater reliability concerns consistency across different observers, not the internal coherence of a set of test items.