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The aim was to compare the psychometric properties of absolute versus differential ratings of the within-family environments and to examine their associations with conduct problems in 8–16-year-old twins.The sample comprised 1117 pairs of like-sex male and female twins and their parents, recruited from the school population of Virginia. The within-family environment was assessed from the Twin Inventory of Relationships and Experiences (TIRE), which provided measures of differential parental criticism, parental preference for one twin, and twins' peers' conduct problems, as rated by mothers, fathers and each of the twins. Twins' conduct problems were assessed by a modified version of the Olweus questionnaire.Although differential ratings and absolute ratings had similar psychometric properties, the use of absolute ratings to differentiate the twins resulted in a construct with weak inter-rater agreement and low stability over time. Differential ratings of the twins' environment showed significant associations with differences in conduct problems between the twins, whereas the difference in absolute ratings of each twin did not. The differential parental criticism effect was uninfluenced by the overall level of criticism in the family.A direct contrast between siblings or twins, as part of the rating procedure (as provided by differential ratings), may be a more efficient way to assess aspects of the within-family environment that are reliable and which are associated with psychopathology. Both differential parental criticism and peers' conduct disturbance were associated with conduct problems in the twins.