g. De Fruyt et al., 2009, Hrebícková et al., 2002 and McCrae et al., 2005). This has led to them being empirically related to a cornucopia of concepts as well as used in mediation and moderation models of current behaviours, helping to define relationships and explain outcomes. In adolescence, personality PI3K inhibitor may even be a key mediator of individual differences in the course and treatment responses of youth with mental disorders that emerge at this period in development (Costello, Copeland, & Angold, 2011). However, on closer inspection, problems remain with personality measurement in adolescents. In comparison to adult research, studies with adolescents have found more cross loadings, and items that

do not load sufficiently on any factor. CDK inhibitor Additionally, the studies demonstrate that items from the Neuroticism and Conscientiousness scales perform better, whereas Extraversion, Agreeableness and Openness items have less reliability (e.g. Parker and Stumpf, 1998 and Sneed et al., 2002). The problems with factor replicability may be due to developmental changes that take place during this time; personality traits are still in flux throughout adolescence (McCrae et al., 2002) and the structure and coherence of the five factors vary at different ages (Soto, John, Gosling, & Potter, 2008). Therefore it is important to

determine if the precision of personality measurement can be maximised for use in behavioural and clinical studies in this age range. Item response theory (IRT) can be used to improve the measurement Buspirone HCl of adolescent personality. The application of IRT allows scale psychometric properties to be revealed with greater precision than other multivariate methodologies; analysing item level information can provide insights into measurement reliability and enables a thorough evaluation of the internal construct validity. IRT provides information by checking the validity of the items and delineating poor performing indicators. It does this by estimating each individual item’s discrimination on the latent trait (the

a parameter) and difficulty within a population (the b parameter) ( Embretson & Reise, 2000). An item’s discrimination reflects how the probability of endorsing an item changes as the level of the underlying trait increases. Thus, highly discriminating items more strongly represent the latent trait. The item’s difficulty corresponds to the likelihood of an individual endorsing it given their level of the latent trait. An item is considered easy if most people endorse it and the difficulty rises as the likelihood of endorsing it decreases. Therefore some items may be easy to endorse even at relatively low levels of the latent trait. IRT also provides estimates of each scale and item’s total information function through total and item information curves (TICs and IICs).