How does the US Preventive Services Task Force grade its recommendations?
Grade A - Strong Recommendation; Good evidence of improved outcomes with benefits that substantially outweigh risks to patients
Grade B - Recommendation; Fair evidence of improved outcomes with benefits that outweigh risks to patients
Grade C - No Recommendation for or against; Fair evidence of improved outcomes with risks and benefits that are similar
Grade D - Recommendation against routine use; Fair evidence of ineffectiveness or risks that outweigh benefits.
Grade I - Insufficient evidence to assess based on power of studies, flaws in study design, or lack of information
What are Levels of Evidence?
A method of ranking the validity of an intervention based on the study design and quality, and the homogeneity of results.
The Oxford Centre for Evidence-based Medicine has a nice table on their webpage...
What is the hierarchy of study design types?
1. Meta-analyses and Systematic Reviews of Randomized Controlled Trials
2. Randomized Controlled Trials
3. Observational Studies (Cohort and Case-Control Studies)
4. Non-experimental Studies (Case Series)
5. Expert Opinion
What is Level 1 Evidence?
1a - Strong evidence from at least one meta-analysis or systematic review of multiple well-designed randomized controlled trials.
1b - Strong evidence from an individual randomized controlled trial with a narrow confidence interval
1c - "All or none" results from a study (i.e. all patients cured from an intervention)
What is Level 2 Evidence?
2a - Strong evidence from at least one meta-analysis or systematic review of multiple well-designed cohort studies.
2b - Strong evidence from an individual cohort study
2c - Outcomes research
What is Level 3 Evidence?
3a - Strong evidence from at least one meta-analysis or systematic review of multiple well-designed case-control studies
3b - Strong evidence from an individual case-control study
What is Level 4 Evidence?
Evidence from non-experimental studies (i.e. case series) and poor quality cohort and case-control studies.
What is Level 5 Evidence?
Opinions of expert committees or respected authorities based on general clinical knowledge, extrapolation of ideas, surrogate outcomes, or principles from bench research.
What is the "gold standard" of study designs?
Double-blinded placebo-controlled randomized clinical trial
However, acheiving the goal of a randomized clinical trial may not be ethical, especially in the context of surgical therapies. In addition, time and costs may be prohibitive.
What is a cohort study?
A study where groups of patients with and without a specified exposure (i.e. Tamoxifen) are followed over a period of time for the onset of a disease (i.e. contralateral breast cancer). This can be defined prospectively or retrospectively.
What is a case-control study?
A study that begins with patients with and without an outcome or disease (i.e. mesothelioma), then examines for possible risk factors (i.e. asbestos exposure, smoking).
What is a cross-sectional study?
A study that summarizes the characteristics of population at a given time, demonstrating both disease and exposure prevalence.
Late... SG
Sources:
US Preventive Services Task Force Guide to Clinical Preventive Services
Oxford Centre for Evidence-Based Medicine
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