The relevance of measuring individual discrimination in personality: A study with the Test Anxiety Scale for Children

• Individuals respond to personality tests with different degrees of discrimination.
• We assessed individual-differences in discrimination using IRT in the TAS-C.
• Measuring discrimination added information and improved trait estimates.
• Individual discrimination worked as a moderator in the anxiety–performance relation.

Personality theorists and researchers have long been aware that individuals respond to personality test items with different degrees of precision. However, standard models in common use in personality assume that the amount of individual discrimination is constant for all respondents. This article applies a simple Item Response Theory (IRT) model with an additional person discrimination parameter to a well-known anxiety measure: the Test Anxiety Scale for Children (TAS-C). The results show that the application is feasible and that the measurement of individual discrimination leads to important advantages both in terms of individual assessment (improved interpretation, differential precision of the estimates) and validity (differential predictability with respect to an external criterion of academic performance).