After identifying an article or resource that seems appropriate to your question, you must critically appraise the information you found. Filtered resources such as DynaMed have often pre-appraised the literature they cite, but primary literature–e.g. individual studies found in a database such as PubMed–are not pre-appraised. Some types of filtered information, such as systematic reviews, critically appraise the studies that they include in their summary of the literature, but you as the reader will also want to critically appraise the methods of the systematic review.
When evaluating the quality of any study, ask yourself the following:
- Does this study address a clearly focused question?
- Does the study use valid methods to address this question?
- Are the valid results of this study important and applicable to my patient, population, or problem?
Just like some fields of study might not be addressed by a systematic review or RCT, some types of questions are better suited to some study types than others.
Below is a table of types of clinical questions and the suggested research design to answer that question, in the order of highest level of evidence to lowest. For example, if your PICO question is about a therapy or intervention to treat a condition, a systematic review or meta-analysis would be the best level of evidence, but if that doesn’t exist then you would want to look for an RCT. If an RCT doesn’t exist, then you would look for a cohort study, and so on.
|Type of Question||Suggested Research Designs|
|All clinical questions||Systematic review, meta-analysis|
|Therapy: Does this treatment work?||Randomized Controlled Trial (RCT) > Cohort Study > Case Control|
|Etiology/Harm: What are the causes of this disease, condition, or problem?||RCT > Cohort Study > Case Control|
|Diagnosis: Which diagnostic test should I use?||RCT > Cohort Study|
|Prevention: How do we reduce the chance of disease by identifying risk factors?||RCT > Cohort Study > Case Control|
|Prognosis: What is the patient/population’s likely course over time?||Cohort Study > Case Control|
|Quality of Life: What will be the patient/population’s quality of life following an intervention?||Qualitative Study|
|Quality Improvement: How can we systematically improve care?||RCT > Qualitative Study|
|Cost: Is one intervention more cost-effective than another?||Economic Evaluation|