Why is a systematic review with quantitative studies considered a high-level, primary source?

A systematic review with quantitative studies is considered a high-level, primary source primarily because it adheres to a predetermined and rigorous research methodology for analysis. This structured approach ensures that the review systematically collects and appraises research evidence, minimizing biases and enhancing the reliability of the conclusions drawn from the data. By employing specific criteria for study inclusion, data extraction, and synthesis of results, the review enables a comprehensive evaluation of the current state of knowledge regarding a particular topic or intervention.

The rigor of the method employed in systematic reviews is what elevates them in the hierarchy of evidence. This quality of adhering to a systematic process is essential for providing robust and trustworthy findings that can inform clinical decision-making and policy.

While peer review is certainly an important aspect of the credibility of research, the systematic and methodical approach that defines systematic reviews stands as the primary reason for their classification as high-level evidence. Additionally, systematic reviews do not focus solely on qualitative data, nor are they merely summaries of existing studies; rather, they synthesize quantitative evidence from multiple studies, making them distinct in their contribution to the research landscape.