Which type of scientific study is referred to as the "diamond standard"?

The term "diamond standard" is commonly associated with systematic reviews, primarily within the context of evidence-based practice. Systematic reviews are rigorous and methodical compilations of research that synthesize findings from multiple studies on a specific question or topic. They ensure the highest level of reliability and validity by establishing a comprehensive framework to evaluate and summarize the existing research.

This type of study is considered the "diamond standard" because it employs a structured approach—typically involving clearly defined criteria for selecting studies, assessing their quality, and synthesizing the evidence. Systematic reviews provide a more cohesive understanding of a research question by evaluating the results and methodologies of various investigations, thereby offering practitioners solid guidance based on a broader pool of evidence.

In contrast, primary studies focus on original research, meta-analysis is a statistical method to combine results from different studies but isn’t inherently a review process, and longitudinal studies track subjects over time to observe changes, rather than synthesizing existing research. Each of these has its merits but doesn’t meet the comprehensive evaluation aspect that characterizes systematic reviews, thus underscoring the latter's status as the "diamond standard."