Oppositional defiant disorder (ODD) is one of the most frequently diagnosed disorders in children with intellectual disabilities (ID). However, the high variability of results in prevalence studies suggests problems that should be investigated further, such as the possible overlap between some ODD symptoms and challenging behaviors that are especially prevalent in children with ID. The study aimed to investigate whether there are differences in the functioning of ODD symptoms between children with (n = 189) and without (n = 474) intellectual disabilities. To do so, we analyzed the extent to which parental ratings on DSM-5 ODD symptoms were metrically invariant between groups using models based on item response theory. The results indicated that two symptoms were non-invariant, with degrees of bias ranging from moderately high ("annoys others on purpose") to moderately low ("argues with adults"). Caution is advised in the use of these symptoms for the assessment and diagnosis of ODD in children with ID. Once the bias was controlled, the measurement model suggested prevalences of 8.4% (children with ID) and 3% (typically developing children). Theoretical and practical implications are discussed.
Keywords: DSM-5; diagnostic overshadowing; dual diagnosis; intellectual disabilities; oppositional defiant disorder.