Studies of individuals with developmental disability and significant speech impairment, defined as speech not adequate to meet daily communication needs, were eligible for inclusion. Studies of individuals with a primary hearing impairment were excluded from the review, as were individuals with an acquired disability. Eligible studies assessed the implementation of AAC, defined as compensation for spoken or written communication through aided or unaided AAC systems, and documented progress in the acquisition of the AAC. Studies were required to report data for speech production, defined as oral expression of language including production of intelligible words or word approximations intelligible in context, before during and/or after acquisition of the AAC. Inclusion criteria for the study design were not reported. The majority of participants in the included studies had learning disabilities, Down syndrome or autism. Both adults and children were included in the studies. The included studies were case studies, pre-test, post-test designs, or variants of n=1 designs. Both aided and unaided interventions with and without speech output were assessed in the included studies.
The authors did not state how the studies were selected for the review, or how many reviewers performed the selection.