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What is an acceptable level of reliability for a psychometric test?

Most psychological societies (e.g., British Psychological Society) and academics (e.g., Devellis, 1991) suggest that an acceptable level of reliability for psychometric tests is:

Ability/Aptitude Tests: .80
Personality Tests: .70

Acceptable and unacceptable levels of the Cronbach’s Alpha coefficient:


Alpha coefficient


implied reliability



below .60




between .60 and .65




between .65 and .70


minimally acceptable


between .70 and .80




between .80 and .90


very good


much above .90


consider shortening the scale


(DeVellis, 1991, p.85)

DeVellis, R.F. (1991). Scale development. Newbury Park, NJ: Sage Publications.