The Factor Structure of the Self-Determination Inventory Portuguese Translation for Persons With and Without Intellectual and Developmental Disabilities: A Confirmatory Analysis.

Background: Self-determination has seen increasing interest in literature worldwide, in terms of its contextualisation, operationalisation and assessment. Developing sound and robust instruments will enable valid assessment both within individual countries and in cross-cultural comparisons.

Methods: The new Self-Determination Inventory (SDI) was translated and adapted into Portuguese, for people with intellectual and developmental disabilities (IDD) and our goal was to analyse the SDI Portuguese Translation's factorial structure. The inventory was administered to 408 participants, between 13 and 73 years old (27 ± 13.6), 246 females and 162 males, with (n = 146) and without IDD (n = 262). Factor structure, measurement invariance and latent difference between persons with and without IDD were analysed.

Results: The confirmatory factor analysis supported the SDI Portuguese Translations' psychometric properties. The data fit a unidimensional model, indicating that the 21 items represent the construct better than a three-factor model. The measurement invariance across groups confirms that the latent construct can be measured and the assessment used with both groups. However, participants with IDD experience greater variability in scores and tend to report lower levels of self-determination.

Conclusions: Findings provide support for the use of SDI Portuguese Translation for persons with and without IDD. Implications for research and practice are discussed.