Convergent validity evidence for the Pain and Discomfort Scale (PADS) for pain assessment among adults with intellectual disability

OBJECTIVES: The main aim of the study was to generate initial convergent validity evidence for the Pain and Discomfort Scale (PADS) for use with nonverbal adults with intellectual disabilities. MATERIALS AND METHODS: Forty-four adults with intellectual disability (mean age=46, 52% male) were evaluated using a standardized sham-controlled and blinded sensory testing protocol, from which Facial Action Coding System (FACS) and PADS scores were tested for (1) sensitivity to an array of calibrated sensory stimuli; (2) specificity (active vs. sham trials); and (3) concordance. RESULTS: The primary findings were those participants who were reliably coded using both FACS and PADS approaches as being reactive to the sensory stimuli (FACS: F2,86=4.71, P<0.05, PADS: F2,86=21.49, P<0.05) (sensitivity evidence), not reactive during the sham stimulus trials (FACS: F1,43=3.77, P=0.06, PADS: F1,43=5.87, P=0.02) (specificity evidence), and there were significant (r=0.41 to 0.51, P<0.01) correlations between PADS and FACS (convergent validity evidence). DISCUSSION: FACS is an objective coding platform for facial expression. It requires intensive training and resources for scoring. As such it may be limited for clinical application. PADS was designed for clinical application. PADS scores were comparable with FACS scores under controlled evaluation conditions providing partial convergent validity evidence for its use.