Evidenced-based practices (EBPs) are generally defined through well-designed, randomized controlled studies. In medicine, randomized controlled trials (RCTs) are the rule rather than the exception; while in the field of IDD, research is often quasi-experimental, correlational, or single-case in design. Using traditional criteria (e.g., gold standard RCTs) to evaluate evidence in the IDD field may limit the utility of the evidence-based practice framework in the IDD field. In the field of intellectual and developmental disabilities, there are few instances where clinical trials are possible, or even necessary. Yet, there are ways to utilize the available knowledge in the design of a IDD system which includes best practice.

In response to the challenges of applying EBPs to the field of IDD, the National Association of State Directors of Developmental Disabilities Services (NASDDDS) and the Association of University Centers on Disability (AUCD) have worked together since 2010 to promote “evidence-based policymaking”. NASDDDS defines evidence-based policy as “the responsible application of the best available evidence in the design, administration, and reform of programs, services, and supports in a manner consistent with achieving independence, productivity, inclusion and self-determination for individuals with developmental disabilities”.

In the field of IDD, the provision of services and supports does not easily fit into a treatment framework because services involve much more than treatment, cure, or the amelioration of symptoms of an illness or disorder. That is why the application of evidence-based practice is often difficult. However, there are some individual treatments which do fit into the EBP paradigm and these should be evaluated. In addition, there are policy practices which may be used to decrease or eliminate the intensity of specific symptoms (rather than the disability in general), teach skills and provide habilitation, implement supports to enhance community participation, and provide support to family members and other stakeholders. Working within an evidence-based framework and making decisions based on the best available data supports the goal of improving lives of individuals with intellectual and developmental disabilities and those who are involved in their lives.