How to find the best evidence?
You will want to use the best evidence for your project. Below is the "Levels of Clinical Evidence" of which you may want to keep in mind while finding resources. Two important elements of the well-built clinical question to consider are the type of foreground question (or clinical category) and the type of study design (methodology) or levels of clinical evidence. This information can be helpful in focusing the question and determining the most appropriate type of evidence.
Look at your clinical research question and locate the Clinical Category below.
Clinical Categories of Primary Question Types
- Therapy: how to select treatments to offer our patients that do more good than harm and that are worth the efforts and costs of using them.
- Diagnostic tests: how to select and interpret diagnostic tests, in order to confirm or exclude a diagnosis, based on considering their precision, accuracy, acceptability, expense, safety, etc.
- Prognosis: how to estimate a patient's likely clinical course over time due to factors other than interventions
- Harm / Etiology: how to identify causes for disease (including its iatrogenic forms).
Other Question Types
- Clinical findings: how to properly gather and interpret findings from the history and physical examination.
- Clinical manifestations of disease: knowing how often and when a disease causes its clinical manifestations and how to use this knowledge in classifying our patients' illnesses.
- Differential diagnosis: when considering the possible causes of our patient’s clinical problem, how to select those that are likely, serious and responsive to treatment.
- Prevention: how to reduce the chance of disease by identifying and modifying risk factors and how to diagnose disease early by screening.
- Qualitative: how to empathize with our patients’ situations, appreciate the meaning they find in the experience and >understand how this meaning influences their healing.
From: Sackett, DL. Evidence-based medicine: how to practice and teach EBM.
Adapted from: Duke University Library
Levels of Clinical Evidence
The higher on the pyramid, there will be fewer studies available and the relevance strength to the cinical question (query) will be greater. As you go down the pyramid, you may see greater bias.
Meta Analysis and Systematic Reviews are filtered studies and are considered secondary evidence. Randomized Controlled Trials are the first of the unfiltered studies and are considered primary evidence study designs.
Levels of Clinical Evidence and Clinical Categories Help with Understanding the Evidence Needed
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Random Controlled Trials (RCTs) answer therapy and diagnosis questions. If a RCT is not found, move down the pyramid to the next best option.
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Cohort Studies help to answer prognosis and etiology/harm questions.
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If you are not finding a Cohort Study to answer prognosis or etiology/harm questions, use a Case Control Study.
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If you cannot find a Cohort or Control Study to answer prognosis or etiology/harm questions, use a Case Series and Reports.
Levels of Clinical Evidence Definitions
Primary types of Research Study Designs
- Systematic review: A review of a body of data that uses explicit methods to locate primary studies, and explicit criteria to assess their quality.
- Randomized Controlled Trials: Individuals are randomly allocated to a control group and a group who receive a specific intervention. Otherwise the two groups are identical for any significant variables. They are followed up for specific end points. They may be
- Double-blind (neither subject nor researcher knows)
- Single-blind (subject doesn’t know which therapy or intervention they have)
- Cohort Studies: Groups of people are selected on the basis of their exposure to a particular agent and followed up for specific outcomes.
- Case Control Studies: Patients ("cases") with the condition are matched with "controls" without, and a retrospective analysis is used to look for differences between the two groups.
- Expert Opinion and Anecdotal: A consensus of experience from the good and the great. Ex: Something someone told you after a meeting.
