DynaMed provides easy-to-interpret Level of Evidence labels so users can quickly find the best available evidence and determine the quality of the best available evidence. Evidence may be labeled in one of three levels:

Level 1 (likely reliable) Evidence - representing the most valid reports addressing patient-oriented outcomes. Examples include rigorous randomized trials, inception cohort studies for prognostic information, and systematic reviews of level 1 evidence reports. Achieving a level 1 evidence label means that specific quality criteria were met based on the study type, and these are detailed further down on this page.

Level 2 (mid-level) Evidence - representing reports addressing patient-oriented outcomes, and using some method of scientific investigation, yet not meeting the quality criteria to achieve level 1 evidence labeling. Examples include randomized trials with less than 80% follow-up, non-randomized comparison studies, and diagnostic studies without adequate reference standards. Level 2 evidence does not imply reliable evidence. For example, hormone replacement therapy was associated with reduced cardiovascular events in large cohort studies (level 2 evidence), but then shown not to be preventive (and possibly increase the cardiovascular risk) in randomized trials (level 1 evidence).

Level 3 (lacking direct) Evidence - representing reports that are not based on scientific analysis of patient-oriented outcomes. Examples include case series, case reports, expert opinion, and conclusions extrapolated indirectly from scientific studies.

Recommendations are labeled as one of the following:

• Grade A recommendation (consistent high-quality evidence)
• Grade B recommendation (inconsistent or limited evidence)
• Grade C recommendation (lacking direct evidence)

This labeling scheme is formally named the Strength Of Recommendation Taxonomy (SORT) and is described in detail, along with the algorithms used for its application, in Am Fam Physician 2004 Feb 1;69(3):548-56.

The United States Preventive Services Task Force (USPSTF) uses a different rating scheme for their recommendations as follows:

A recommendation = USPSTF strongly recommends that clinicians provide the service to eligible patients, based on good evidence that the service improves important health outcomes and that benefits substantially outweigh harms.

B recommendation = USPSTF recommends that clinicians provide the service to eligible patients, based on at least fair evidence that the service improves important health outcomes and that benefits outweigh harms.

C recommendation = USPSTF makes no recommendation for or against providing the service, based on at least fair evidence that the service can improve health outcomes but the balance of benefits and harms is too close to justify a general recommendation.

D recommendation = USPSTF recommends against routinely providing the service to asymptomatic patients, based on at least fair evidence that the service is ineffective or that harms outweigh benefits.

I recommendation = USPSTF concludes that the evidence is insufficient to recommend for or against routinely providing the service, based on evidence that is lacking, of poor quality, insufficient, or unable to determine the balance of benefits and harms.

DynaMed criteria for level 1 (likely reliable) evidence labels

• DynaMed criteria for level 1 (likely reliable) evidence for a randomized trial
  1. Full-text report available in English (or language well understood by participating editor)
  2. Clinical outcome (also called patient-oriented outcomes)
  3. Random allocation method (i.e. not assigned by date of birth, day of presentation, “every other”)
  4. Allocation concealed
  5. Blinding of all persons (patient, treating clinician, outcome assessor) if possible
  6. Intention-to-treat analysis comparing groups according to randomization
  7. Follow-up (endpoint assessment) of at least 80% of study entrants AND adequate such that losses to follow-up could not materially change results
  8. Adequate statistical power
  9. In cases of early trial termination
     1. Stopping decision made by independent monitoring board without competing interests
     2. Interim analysis is preplanned
     3. Statistical stopping rule accounts for multiple assessments (lower p value threshold) for early termination for benefit
     4. Clinically significant differences with absolute benefit/harm warranting early termination
  10. No other factors contributing substantial bias, such as
      1. Differences in management between groups other than the intervention being studied
      2. Differential loss to follow-up
      3. Posthoc analysis
      4. Subgroup analysis
      5. Baseline differences between groups
      6. Unclear how missing data is accounted for
• DynaMed criteria for level 1 (likely reliable) evidence for a systematic review
  1. Full-text report available in English (or language well understood by participating editor)
  2. Clinical outcome (also called patient-oriented outcomes)
  3. Systematic search
  4. Explicit inclusion criteria
  5. Systematic selection of included studies
  6. Evaluation of study quality
  7. Additional criteria if meta-analysis
     1. Studies are clinically appropriate for pooled analysis (reasonably similar populations, interventions, methodology and outcomes)
     2. Meta-analysis not limited by statistically significant heterogeneity
  8. Conclusion based on primary studies meeting Level 1 evidence criteria
  9. Adequate statistical power
  10. No other factors contributing substantial bias, such as
      3. Inclusion criteria that appear to inappropriately exclude important evidence
      4. Subgroup analysis
      5. Indirect comparisons
• DynaMed criteria for level 1 (likely reliable) evidence for a diagnostic cohort study
  1. Full-text report available in English (or language well understood by participating editor)
  2. Patient sample represents patients for whom testing would be appropriate (i.e. diagnostic uncertainty)
  3. Reliable reference standard
  4. Reference standard and test under investigation each applied to all study subjects (with and without diagnosis)
  5. Test under investigation conducted blinded to and independent of reference standard results
  6. Reference standard conducted blinded to and independent of study test results
  7. Adequate follow-up and accounting for subjects
  8. Adequate statistical power
  9. No other factors contributing substantial bias
• DynaMed criteria for level 1 (likely reliable) evidence for a prognosis study
  1. Full-text report available in English (or language well understood by participating editor)
  2. Inception cohort study
  3. Prospective follow-up
  4. Representative sample at similar point in course of disease
  5. Follow-up sufficiently long and complete
  6. Systematic (unbiased) evaluation of outcomes
  7. Adjustments for important confounding factors
  8. Adequate statistical power
  9. No other factors contributing substantial bias
• DynaMed criteria for level 1 (likely reliable) evidence for prediction rules
  1. Validation in relevant population
  2. Validation in sample independent from derivation cohort
  3. Use appropriate criteria list for diagnostic or prognostic study