Reliability and Validity of the Diagnostic Instrument on Adaptive Behaviour: A New Instrument Measuring Adaptive Behaviour in People With Moderate, Severe or Profound Intellectual Disability.

BACKGROUND: Assessment of adaptive behaviour of people with moderate to profound intellectual disability is hampered by limited variation in scores within this range. We evaluated measurement properties of the Diagnostic Instrument on Adaptive Behaviour (DIAB), which was developed for this population. METHOD: The DIAB was completed by two care staff members for 73 adults (age 19-84) grouped by level of intellectual disability (i.e., moderate, severe or profound intellectual disability) along with Dutch normed measures of adaptive and motor functioning and a global rating. RESULTS: Inter-rater (ICC = 0.94) and test-retest (ICC = 0.96) reliability met standards. DIAB scores correlated highly with those of the two Dutch instruments (r = 0.90; r = 0.77). Associations between measures were consistent with convergent and discriminant validity. DIAB scores differed between three severity levels of ID (p < 0.001). CONCLUSION: The DIAB exhibited promising reliability, convergent, discriminant, concurrent, and known group validity.