This means IRT can be used to reveal how informative a measure is at all levels of the latent trait ( Baker, 2001). Although IRT can be used to assess the internal validity of a measure, correlates are needed to examine the impact on external validity. IRT analysis has been conducted with adult samples and shows that when check details the best performing items are chosen, shortened versions of personality inventories often have similar predictive capabilities (Thalmayer, Saucier, & Eigenhuis, 2011). Indeed, Reise and Henson (2000) found that after IRT the NEO-PI-R could be

greatly reduced and for many scales only the best four items were needed to produce comparable facet results. Such psychometric research has however not been carried out with younger populations. As well as delineating internal construct validity MAPK inhibitor this study uses several measures to examine external criterion validity including educational performance, current friendships and general well-being. These measures cover the domains of adolescent competence which are important for the successful negotiation of developmental tasks (Masten et al., 1995). Each personality trait is hypothesised to correlate to varying degrees with the different facets of adolescent competence and therefore go some way towards highlighting a personality pattern associated with individual differences in

competent adolescent functioning. It is hypothesised that Extraversion and Conscientiousness will be positively and Neuroticism

negatively associated with well-being (Siegler & Brummett, 2000). Likewise, elevated levels of Conscientiousness and Openness will be associated with school performance (Chamorro-Premuzic and Furnham, 2003 and De Fruyt et al., 2008). Finally we will examine whether Extraversion and Agreeableness are associated with the quality of current friendship (Scholte et al., 1997 and Selfhout et al., 2010). This study applies IRT methodology to the NEO-FFI in order to investigate how it can be utilised to improve the validity of personality measurement in a late adolescent population. Furthermore, an examination of external validity will explore which personality traits are associated with adolescent competence as indexed by measures of current well-being, friendships and school examination performance. Montelukast Sodium Participants were 470 English adolescents (295 females, 175 males) who completed the NEO-FFI; mean age 18.7 years (age range: 17.7–20.2 years, SD = 0.55). The participants are part of the ongoing ROOTS study; a longitudinal study of 1204 participants aged 14 years at first recruitment and reassessed at 15.5 and 17.5 years (Goodyer, Croudace, Dunn, Herbert, & Jones, 2010). At 17.5 years data were gathered about academic achievement; additionally participants completed a friendship satisfaction questionnaire (Goodyer, Wright, & Altham, 1989) and the Warwick–Edinburgh Mental Well-being Scale (WEMWBS; Tennant, Fishwick, Platt, Joseph, & Stewart-Brown, 2006).