be evaluated by personality assessments. van den Berg et al.41 applied IRT to the attention problems subscale of the Young Adults Self Report questionnaire42 assessed in a sample of individuals from the Netherlands Twin Registry. Heritability of the estimated latent trait was found to be much larger than the heritability of the traditionally used sum score: 73% vs 40%, respectively. Using IRT in samples evaluated with different personality assessments would identify a subset of items in these different instruments that are related to a common, unmeasured latent trait. Samples measured with multiple instruments are needed to identify these items, which are then extracted from samples evaluated using only one instrument. Refinement of personality phenotypes in this manner has the potential to greatly improve power to genetically map these traits.
