What does Cronbach's alpha measure?

Cronbach's alpha is a statistic that assesses the internal consistency or reliability of a set of items in a test or questionnaire. Specifically, it measures the mean correlation among the items, which indicates how closely related the items are as a group. A higher Cronbach's alpha suggests that the items measure the same underlying construct and are therefore reliable.

This focus on the mean correlation among items is crucial in understanding how well the items work together to reflect the construct being measured, which is essential for ensuring that the test produces consistent results across different administrations and populations.

The other options do not capture the essence of what Cronbach's alpha assesses. The overall score of the test (the first option) relates to the total performance of an individual on the test and does not reflect the correlation between items. While the reliability of a test across various situations (the third option) is related to the concept of reliability, Cronbach's alpha specifically addresses internal consistency rather than external reliability across different situations. The number of items in a test (the fourth option) does not provide insight into how closely those items work together in measuring a construct.