Reliability and Validity of the Supplemental Protection and Advocacy Scale of the Supports Intensity Scale

Three separate studies were undertaken to examine the reliability and validity of the Supplemental Protection and Advocacy Scale (P&A Scale) of the Supports Intensity Scale (SIS). In Study 1, the interrater reliability of the P&A Scale was investigated when interviewers were trained in SIS administration and scoring. Pearson's product moment coefficients were considerably higher than coefficients reported in a previous study conducted with untrained interviewers. In Study 2, the reliability (internal consistency, standard error of measurement, and interrater reliability) and validity (content and construct validity) of the P&A Scale when administered by trained interviewers with a sample of individuals with intellectual disability and related developmental disabilities (ID/DD) receiving services from a state ID/DD agency were examined. Results indicated strong reliability and validity of the P&A Scale, comparable to other domains of the SIS. In Study 3, additional psychometric properties of the P&A Scale were examined in a large sample of trained interviewers from across the United States and Canada using the SIS Online, with findings again showing strong psychometric properties. Collectively, findings from these three investigations suggested that the P&A Scale is a reliable and valid measure of support needs. In future revisions of the SIS, the P&A Scale should be considered for inclusion in the section of the SIS that yields standard scores reflecting an individual's relative intensity of support need.