We describe the factor structure of IPIP Big-Five factor markers in self-reports and parental ratings of a large sample of children and adolescents in Croatia using cross-sectional and longitudinal data, respectively. The International Personality Item Pool (50 items) is a cross-cultural instrument targeted to measure the Big-Five domains, adapted for child and adolescent ratings in this study. A large sample of children and adolescents in Croatia (N≈ 1900), aged from 9 to 19 years used the IPIP50 to rate themselves (self-ratings) and they were also rated by their parents (parental-ratings). A part of children and adolescent sample provided the ratings once more 18 months after the first testing. Concerning the cross-sectional data, we performed the exploratory as well as the confirmatory factor analyses to determine the structure and factorial invariance across different age groups for self-ratings and parental ratings, respectively. The structure of the self-ratings and the model fit in the younger age groups (9-12 years) showed a somewhat greater departure from the Big-Five. The structure of the self-ratings in the groups older than 13 years as well as the model fit was comparable with the parental ratings. Concerning the longitudinal data, the changes in the stability of the factor structure are discussed. The results are interpreted from two perspectives: 1) IPIP Big-Five markers can be used as a self-report measure after the age of 13, however with further psychometric refinement and 2) there is a need to develop special forms of IPIP50 for younger age groups |