Psychometric properties of the Beliefs About Adults with ID Scale in American physicians: Application of classical test and Rasch measurement theories

Background: Physicians' erroneous assumptions about individuals with intellectual disability (ID) negatively impact the quality of care provided to this population. This study aimed to investigate the psychometric properties of the Beliefs About Adults with ID (BAID), an instrument we developed for measuring physicians' erroneous assumptions about adults with ID. Methods: Two hundred ninety-two American physicians participated. Classical test theory and Rasch measurement theory were used to refine the scale (through item analysis, exploratory factor analysis, infit and outfit mean-squares statistics, and differential item functioning) and investigate its psychometric properties (functioning of the response scale, reliability, and validity). Results: The BAID provided a unidimensional, reliable, valid, and precise measure in assessing high levels of erroneous assumptions. It showed convergent and divergent validity with the different factors of a scale measuring attitudes towards ID. The BAID items were discriminant, non-redundant, unambiguous, and invariant across gender and previous ID training. The BAID response scale was found to be appropriate for measuring physicians' erroneous assumptions about adults with ID. Conclusions: BAID is a brief instrument with good psychometric properties to assess erroneous assumptions about adults with ID in physicians of different genders and who have/have not previously received ID training. Therefore, it might be helpful for research and medical education purposes.