Item response theory and validity of the NEO-FFI in adolescents

► It is important to maximise the precision of personality measurement in adolescents. ► We apply item response theory (IRT) to the NEO-FFI in an adolescent sample. ► IRT was used to assess item validity and highlight poorly performing indicators. ► Removing poor items reduced measurement error without compromising validity. ► IRT analysis can be used to develop personality measures ensuring item validity.