| Fear and fearlessness are related trait dispositions that have been investigated at their extremes with respect to distinctive variants of psychopathology, anxiety disorders and psychopathy, respectively. A commonly associated neural substrate of fear-related disorders is defensive reactivity reflected in the fear-potentiated startle (FPS) response. In order to help bridge these literatures by delineating the phenotype that variation in FPS may reflect, a number of questionnaire measures assessing traits previously associated with this neurobiological response were administered to a community-dwelling sample of twins. The findings of Study 1 revealed a hierarchical structure to the trait fear domain, with a single, bipolar dimension accounting for the shared variance among the measures, and subfactors labeled 'distress,' 'stimulation seeking,' and 'sociability' varying independently of the general factor. The structure of genetic and non-shared environmental associations among the measures closely mirrored the phenotypic structure of the domain. The aim of Study 2 was to develop a self-report inventory comprising a unique set of items to index variation in the general factor of the structural model elucidated in Study 1. A set of items from the measures used in the first study served to 'anchor' parameter estimates of the twin and student samples for analyses evaluating candidate inventory item properties in the student sample. Psychometric procedures of Classical Test and Item Response Theories were utilized in the construction of the Trait Fear Inventory, and associations between scores on this measure, the anchor items, and the general fear/fearlessness factor indicated a high degree of success in capturing variation in the latter with an entirely independent set of items. |
