Cronbach's alpha (α)

Cronbach's alpha is a statistical measure of internal consistency reliability. It estimates how closely related the items on a scale are as a group, ranging from 0 (no consistency) to 1 (perfect consistency).

Values of 0.7 or above are typically considered acceptable, 0.8 or above good, and 0.9 or above excellent — though very high values can also indicate redundant items. Most peer-reviewed psychology assessments report Cronbach's alpha for each subscale; published values let researchers and clinicians judge how trustworthy a score is.