Purpose: This study was designed to translate and assess the psychometric properties of Supports Intensity Scale among adults with intellectual and developmental disability in Ahvaz and Tehran, Iran.Method: The cross-sectional study was carried out in two stages.  The first stage consisted of the forward-backward translation of Supports Intensity Scale - Adult Version) SIS-A(. In the second stage, 197 people with intellectual and developmental disabilities were recruited in order to assess the internal consistency and test-retest reliability, concurrent and content validity of SIS-A. The confirmatory factor analysis (CFA) was performed to approve the seven-factor model of the instrument.Results: The intra-class correlation coefficient values varied between 0.85 and 0.99 (very good to excellent). All subscales of the SIS-A showed Cronbach’s alpha above 0.70. Correlation coefficient between SIS-A and Barthel index was about -0.65, which shows excellent concurrent validity of SIS-A. The findings showed SIS-A had high ability to discriminate between groups with different IQ (p<0.05). There was no significant correlation between SIS-A and the age of participants (p>0.05). The result of CFA confirmed that the seven-factor model of SIS-A is the fittest pattern for SIS-A.Conclusion: The results indicated that the Persian version of SIS-A is a valid and reliable instrument to assess function and disability among people with intellectual and developmental disability.

Purpose:This study was designed to translate and assess the psychometric properties of Supports Intensity Scale among adults with intellectual and developmental disability in Ahvaz and Tehran, Iran. Method:The cross-sectional study was carried out in two stages. The first stage consisted of the forward-backward translation of Supports Intensity Scale -Adult Version) SIS-A). In the second stage, 197 people with intellectual and developmental disabilities were recruited in order to assess the internal consistency and test-retest reliability, concurrent and content validity of SIS-A. The confirmatory factor analysis (CFA) was performed to approve the sevenfactor model of the instrument. Results:The intra-class correlation coefficient values varied between 0.85 and 0.99 (very good to excellent). All subscales of the SIS-A showed Cronbach's alpha above 0.70. Correlation coefficient between SIS-A and Barthel index was about -0.65, which shows excellent concurrent validity of SIS-A. The findings showed SIS-A had high ability to discriminate between groups with different IQ (p<0.05). There was no significant correlation between SIS-A and the age of participants (p>0.05). The result of CFA confirmed that the seven-factor model of SIS-A is the fittest pattern for SIS-A. Conclusion: The results indicated that the Persian version of SIS-A is a validand reliable instrument to assess function and disability among people with intellectual and developmental disability.