Quality and Strength of Evidence

Quality of Study Design

The quality of a study is…“the extent to which a study’s design, conduct, and analysis has minimized selection, measurement, and confounding biases (Lohr KN, Carey TS. Joint Commission Journal of Quality Improvement. 1999, vol. 25, 470-479)

Quality assessment is well established in systematic reviews of randomized controlled trials.”…However, “As no gold standard exists, researchers either ignore the issue or develop their own tools” (Mallen et al., Journal of Clinical Epidemiology. 2006, vol. 59, 765-769)

For more information on how to assess the quality of the study design:

Paper presented at the Annual Meeting of the Association for the Advancement of Educational Research (AAER) (Ponte Vedra, FL, November 2000).
Expanding the Framework of Internal and External Validity in Quantitative Research

Or read: Experimental and Quasi-experimental Designs for Research by Donald T. Campbell and Julian Stanley

Rating the Strength of Evidence

Methodologists and guideline developers have given much thought and effort to considering the criteria and approaches to an optimal method for rating the strength of evidence. Below are two approaches to rating the strength of evidence.

For more information about methods to rate the strength of evidence:

AHRQ: Systems to Rate the Strength of Evidence

Grading quality of evidence and strength of recommendations.

Grading Strength of Recommendations and Quality of Evidence in Clinical Guidelines