Evaluating the Inter-Respondent (Consumer vs. Staff) Reliability and Construct Validity (SIS vs. Vineland) of the Supports Intensity Scale on a Dutch Sample

Background: Despite various reliability studies on the Supports Intensity Scale (SIS), to date there has not been an evaluation of the reliability of client vs. staff judgments. Such determination is important, given the increasing consumer-driven approach to services. Additionally, there has not been an evaluation of the instrument's construct validity on a non-English speaking sample. This is important as the SIS is currently translated into 13 languages. Method: Data were collected in two different samples, using the Dutch translation of the SIS and the Vineland-Z. Results: There was a significant correlation between ratings of staff and consumers on the SIS; however, the relationship between the mean scores of consumer and staff responses indicated significant differences in staff and consumer scores. All correlations between the Vineland-Z domains and the SIS subscales were significant and negative, ranging from -0.37 to -0.89. Conclusions: Analyses of the inter-respondent reliability suggest that one needs to consider the source of information regarding needed supports carefully. The significant negative correlations between SIS and Vineland-Z reflect that the SIS is measuring a different construct (needed support) than the Vineland-Z (adaptive behaviour). The results of the two studies provide additional support for the etic (universal) properties of the SIS, as both hypotheses were confirmed. In conclusion, SIS users are provided with a wealth of information that can be used for multiple purposes.