This study aimed to discover whether general receptive vocabulary is qualitatively phenotypical in Down syndrome. Sixty-two participants with Down syndrome (M age  =  16.74 years, SD  =  3.28) were individually matched on general vocabulary raw total score with 62 participants with intellectual disability of undifferentiated etiology (M age  =  16.20 years, SD  =  3.08) and 62 typical children (M age  =  5.32 years, SD  =  0.82). Item analyses using the transformed item difficulties method to detect differential item functioning across groups showed that the groups' rank orders of item difficulty were highly similar. It was concluded that the general receptive vocabulary of older children and adolescents with Down syndrome is not qualitatively distinguished when its overall size is held constant. Methodological and theoretical implications of this finding are discussed.

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