Circular instead of hierarchical: methodological principles for the evaluation of complex interventions

Area of Science:

• Medical research methodology
• Evidence-based medicine evaluation

Background:

• A hierarchy of evidence, from case studies to blinded randomized controlled trials (RCTs), guides medical intervention evaluation.
• This hierarchy, based on a pharmacological model, is often generalized to complex non-pharmacological interventions like surgery and acupuncture.
• Rigorous RCTs are crucial for removing bias and form the basis for meta-analyses and systematic reviews.

Purpose of the Study:

• To critically assess the limitations of the traditional Evidence Hierarchy for evaluating complex medical interventions.
• To propose an alternative model that better accommodates the complexities of non-pharmacological and multifaceted treatments.

Main Methods:

• The study critiques the applicability of the established Evidence Hierarchy.
• It highlights the inherent conflict between internal validity (bias reduction) and external validity (generalizability) in evaluating complex interventions.
• A conceptual shift towards a more flexible evaluation framework is discussed.

Main Results:

• The hierarchical model is effective for assessing simple efficacy, particularly for regulatory purposes and pharmacological agents.
• It proves inadequate for complex interventions such as physiotherapy, surgery, and complementary and alternative medicine (CAM).
• The tension between internal and external validity limits the universal applicability of the hierarchy.

Conclusions:

• A Circular Model is proposed as a superior alternative to the Evidence Hierarchy for complex interventions.
• This model advocates for a multiplicity of research designs, balancing their respective strengths and weaknesses.
• The Circular Model aims to generate pragmatic, rigorous evidence to support clinical and health systems innovation and evidence-based health reform.