CPIC assigns levels to the evidence linking genotype to phenotype. The literature-based evidence summarized in each guideline’s supplement is graded¹ on a scale of high, moderate and weak, defined as follows:
High: Evidence includes consistent results from well-designed, well-conducted studies.
Moderate: Evidence is sufficient to determine effects, but the strength of the evidence is limited by the number, quality or consistency of the individual studies, generalizability to routine practice, or indirect nature of the evidence.
Weak: Evidence is insufficient to assess the effects on health outcomes because of limited number or power of studies, important flaws in their design or conduct, gaps in the chain of evidence, or lack of information.
¹ Valdes R, Payne DA, Linder MW. Laboratory analysis and application of pharmacogenetics to clinical practice. The National Academy of Clinical Biochemistry (NACB) – Laboratory Medicine Practice Guidelines. Washington, DC2010.