Drop-out during a randomized trial with adolescents with intellectual disability was associated with participant burden, while drop-out at study exit was associated with carer and household characteristics.

Background: People with intellectual disability are difficult to retain in longitudinal studies. Research on determinants of study retention for individual-carer dyads, and their reasons for drop-out, are limited.

Aims: To investigate characteristics associated with drop-out, and to investigate whether characteristics varied by stage of drop-out.

Methods And Procedures: Data are from an Australian randomized trial with adolescents with intellectual disability living in the community. Characteristics of both the adolescent and their nominated carer were collected at baseline. Carers were sent an exit questionnaire approximately two years after enrolment.

Outcomes And Results: Baseline information was available for 566 adolescents: 72(13.0%) withdrew during the study, and 96(17.3%) didn't return exit questionnaires. Characteristics associated with drop-out during the study were being in the intervention group, the carer being younger, and the carer not being one of the adolescent's parents. Characteristics associated with withdrawal at exit were carer having lower education and carer having lower socioeconomic status. No adolescent characteristic was associated with drop-out.

Conclusions And Implications: Characteristics of drop-outs weren't related to the adolescent and differed according to timing. Drop-out during the study was associated with study burden, whereas characteristics of drop-outs at exit interview were associated with lower social position.