Cronbach's alpha is used to assess

• A. Internal consistency
• B. Test-retest reliability
• C. Validity
• D. Diagnostic utility

Answer: (A)

Cronbach's alpha is a statistic used to measure internal consistency—the extent to which items on a scale all tap the same underlying construct. When a multi-item questionnaire aims to assess a single trait or concept, you want the items to behave as a coherent group, showing that they share common variance. Cronbach's alpha does this by examining the average inter-item correlations and the number of items; as the items align more closely with one another, the alpha increases, indicating the scale is functioning as a unified measure. A higher alpha suggests the total score derived from adding or averaging the items is more reliable as an index of that construct.

This focus on how items relate to each other is different from other reliability and validity notions. Test-retest reliability concerns stability of scores over time, so it requires administering the same scale on two occasions. Validity asks whether the scale actually measures the intended construct, which is about meaning and accuracy rather than how consistently items relate. Diagnostic utility involves how well the tool aids in identifying a condition, which depends on thresholds and decision rules beyond internal consistency.

In practice, a reasonable Cronbach's alpha supports aggregating item responses into a single score, but researchers also watch for redundancy—very high values can indicate items are duplicative rather than adding new information.