[Cluster randomised trials: an important method in primary care research]

Area of Science:

• Primary care research
• Health services research
• Clinical trial methodology

Context:

• Interventional studies in primary care frequently involve organizational or educational changes, particularly for guideline implementation.
• Pragmatic considerations often lead to randomisation at the practice level rather than the individual patient level.
• This practice-level randomisation forms clusters of patients, violating the independence assumption crucial for standard statistical analysis.

Purpose:

• To provide insights into the advantages and disadvantages of cluster randomisation.
• To discuss the practical significance of cluster randomisation in the planning and analysis of trials.
• To illustrate these concepts using examples from two cluster randomised trials.

Summary:

• Cluster randomisation, where groups (clusters) like medical practices are randomised, is a common approach in primary care research for interventional studies.
• This method, while pragmatically necessary, leads to patient samples that are not independent, necessitating larger sample sizes and more complex statistical analyses.
• The article examines the benefits and drawbacks of this design, highlighting its importance for effective trial planning and data interpretation.

Impact:

• Enhanced understanding of cluster randomisation methodologies in primary care research.
• Improved planning and analysis strategies for future interventional studies using cluster designs.
• Guidance for researchers navigating the complexities of non-independent patient samples in group-randomised trials.