Comparative research in the field of complex disability following ABI poses several major challenges (Turner-Stokes 2004):
- There is marked heterogeneity with respect to the patient group, the intervention, the setting, and the outcomes that are relevant at each stage of recovery.
- The application of randomized controlled trial (RCT) designs is limited by small numbers of patients at each site, and by ethical considerations because many patients with ABI lack the mental capacity to give fully informed consent.
- Lack of Equipoise: the expanding body of evidence for effectiveness of multidisciplinary rehabilitation in other conditions, particularly stroke, makes it increasingly unethical to randomize patients to 'no treatment' or even 'standard' care.
- The length of time over which rehabilitation may have its effects, often months or years, is typically longer than the funding for research projects and hinders the use of 'wait-list' control groups.
As a result of these challenges, there are few large experimental design studies in this field. Current trends towards the acceptance of RCTs as the gold standard source of evidence may limit the knowledge base needed to make sound decisions about ABI rehabilitation priorities and policies. Given the existing literature base for ABI rehabilitation, evidence-based rehabilitation must rely on a variety of types of evidence, often in combination (Victora et al. 2004) and rigorous observational alternatives to the RCT are still of significant value (Whyte 2002). The inclusion of alternate study designs can provide a more complete picture of the existing evidence, particularly where RCTs are lacking, and thereby advise ABI practice, albeit not as strongly. Excluding data collected under other research designs could bias the evidence base toward interventions that are “easier” to evaluate but not necessarily more effective or cost-effective (Des Jarlais et al. 2004).