Reliability

Key psychometric requirements for patient-reported outcome measures (PROMs) include reliability, validity, and sensitivity to detect change. There are two types of reliability. The first, internal consistency, refers to how people respond to individual items designed to measure the same underlying construct. PROMs often consist of multiple items that are designed to measure the same underlying construct. As such, people’s responses to these items should be consistent. When this is the case, the measure can be said to have internal consistency. This is tested through Cronbach’s alpha. Cronbach’s alpha is a coefficient of reliability or consistency and is a function of the number of test items and the average intercorrelation among the items. The second form of reliability is test-retest reliability. If a measure is administered twice, within a short period of time, it would be expected that a person’s score remains the same. The strength of correlation between the two scores is how we assess test-retest reliability. Measures need to be reliable, producing consistent scores.