inventories, some participants must have filled in multiple inventories so that they can function as a “bridge” between inventories. This can be done if we assume that the true phenotype (personality) does not change between the multiple assessments. If this can be assumed, then for all individuals in the different (sub-)cohorts, a score on the latent construct can be estimated based on all available item data for that person. The IRT-based score estimates for Neuroticism and Extraversion can subsequently be meta-analyzed to assess heritability, or can be used as phenotypes in GWA or brain-imaging studies.
