Purpose The purpose of this paper is to introduce practitioners to the appropriate use of measures of unethical behaviour, evaluate the use of integrity‐related assessments for use in personnel selection, and determine the validity of the moral competency index (MCI) instrument using standard validation procedures. Design/methodology/approach Content, construct, convergent and discriminant approaches are applied to establish the relative validity of the assessment tool. Findings The results of the MCI purport to align with one's moral values and behaviours. The paper establishes face validity of the MCI measure, but fails to establish an appropriate simple factor structure, convergent validity, discriminant validity, and support for the lack of impact of demographic factors on the purported measure of moral intelligence. Research limitations/implications An acceptable but constrained (working students) sample was used in the validation. Practical implications Researchers and practitioners should be familiar with psychometric principles to ensure the use of valid tools in a predictive and defensible manner. New measures can be developed, but should be validated before being used for developmental or personnel decision‐making purposes. Originality/value This paper establishes the lack of validity associated with the MCI instrument; researchers and practitioners are exposed to considerations in the appropriate use of measures of unethical behaviour, and exposed to several previously validated integrity‐related assessments for use in personnel decision‐making.