Can Multi-Item Measures and Single-Item Measures be Trusted to Assess Self-Determination Theory Constructs in the Elderly?

Background: Measuring complex constructs, such as those from self-determination theory models, is challenging in the elderly due to the response process, particularly in collective data gathering. In order to examine this construct in physical activity settings we aimed at determining whether single-item measures were as good as pre-existing multi-item measures. For that reason, we developed seven single-item measures targeting perceived interpersonal styles, basic needs satisfaction, and well-being. Method: We gathered evidence of validity and reliability for multi-item measures and single-item measures based on a sample of 128 elderly adults. Another sample of 62 elderly adults provided test-retest reliability for the single-item measures. Results: Favourable evidence of the expected internal structure, concurrent validity, and reliability was obtained for competence-and relatedness-supportive styles, and for satisfaction of the basic psychological need of relatedness, fairly good evidence was obtained for subjective vitality, whereas mixed evidence was obtained for autonomy-supportive style and the satisfaction of the basic psychological needs of autonomy and competence. Conclusions: Single-item measures proved to be psychometrically sound substitutes for their multi-item counterparts, but the autonomy constructs need to be reconsidered. Furthermore the response process and consequences of testing should play a prominent role when devising questionnaires for the elderly.