Evidence-Based Medicine Study Types
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Type of Study: Treatment
Was it a controlled trial and were the patients randomly assigned? Studies not meeting both criteria are not reviewed.
Are the patients in the study so dissimilar to typical primary care patients that the results will not apply? Studies performed on patients enrolled in settings markedly different from primary care will not be reviewed.
Were steps taken to conceal the treatment assignment from personnel entering patients into the study? “Concealed allocation” through the use of opaque envelopes, centralized randomization, or other methods prevents selective enrollment of patients into a study. It is not the same as blinding, which occurs after the study begins. The primary concern is about who will be enrolling patients. While the investigators are enrolling patients before the trial starts, they should make sure patients do not know to which group they will be allocated. This knowledge might introduce bias and affect how patients are enrolled. Concealed allocation generally will be noted in POEMs reviews but not in Evidence-Based Practice. If the allocation concealment is unclear, the study will be included unless there is a good chance that unconcealed allocation could produce a systematic bias (e.g., when popular opinion favors one treatment over another or when a skewed distribution of disease severity may affect the study outcome).
Were all patients who entered the trial properly accounted for at its conclusion? Follow-up of patients entering the trial will be assessed. Studies with incomplete follow-up or large dropout rates (more than 20 percent) will not be reviewed.
Type of Study: Diagnosis
What is the disease being addressed? Studies evaluating a diagnostic test that identify an abnormality but not a disease generally are not reviewed.
Is the test compared with an acceptable “gold standard”? The characteristics of the new test should be compared with the best available method for identifying the disease.
Were both tests applied in a uniformly blind manner? This question determines that every patient received both tests, and that one test was not performed with knowledge of the results of the other test, which could introduce bias.
Is the new test reasonable? Studies that evaluate diagnostic tests that cannot be implemented readily by primary care physicians will not be reviewed.
What is the prevalence of disease in the study population? The prevalence of disease in the study population will be reported so that readers can compare it with their own practice.
What are the test characteristics? The sensitivity, specificity, predictive values, and likelihood ratios will be reported. These values will be calculated from data in the study if they are not reported by the authors.
Type of Study: Systematic Reviews
Were the methods used to locate relevant studies comprehensive and clearly stated? Reviews not stating the method of locating studies will not be reviewed.
Were explicit methods used to select studies to include in the overview? Reviews not stating methods of including or excluding studies will not be reviewed.
Was the validity of the original studies included in the overview appropriately assessed? Reviews not stating the method used to assess the validity of the original studies will not be reviewed. Reviews can include or exclude studies based on quality scores. Reviews including all studies irrespective of their quality scores should present the validity evaluation; reviews eliminating studies based on low quality should describe explicitly how these studies were eliminated.
Was the assessment of the relevance and validity of the original studies reproducible and free from bias? Published methods of assessing relevance or validity of others can be referenced or new criteria can be described. Generally, validity assessment should be performed independently by at least two investigators.
Was variation between the results of the relevant studies analyzed? Heterogeneity in study results should be evaluated and, if present, explained.
Were the results combined appropriately? When results from different studies are combined, only similar outcomes should be combined. Reviews that attempt to convert study results from one scale to another generally will not be considered.
Type of Study: Prognosis
Was an “inception cohort” assembled? Did the investigators identify a specific group and follow it forward in time? Studies that do not meet these criteria or assemble an “inception cohort” or follow a specific group forward are not reviewed.
Were the criteria for entry into the study objective and reasonable? Entry criteria must be reproducible and not too restrictive or too broad.
Was group follow-up adequate (at least 80 percent)?
Were the patients similar to those in primary care in terms of age, sex, race, severity of disease, and other factors that might influence the course of the disease?
Where did the patients come from—was the referral pattern specified? The source of patients will be noted in the review.
Were outcomes assessed objectively and blindly?
Were all important strategies and outcomes included? Analyses evaluating only some outcomes or strategies will not be reviewed.
Was an explicit and sensible process used to identify, select, and combine the evidence into probabilities? Is the evidence strong enough?
Were the utilities obtained in an explicit and sensible way from credible sources? Specifically, were utilities obtained from small samples or from groups not afflicted with the disease or outcome.
Was the potential impact of any uncertainty in the evidence determined? It must be noted whether a sensitivity analysis was performed to determine how robust the analysis is under different conditions.
How strong is the evidence used in the analysis? Could the uncertainty in the evidence change the result? It will be noted if any given variable unduly influences the analysis.
Was the appropriate method used to answer the question? Interviews or focus groups should be used to study perceptions. Observation is required to evaluate behaviors. Studies not using the appropriate method will not be reviewed.
Was appropriate and adequate sampling used to get the best information? Random sampling is not used in qualitative research. Instead, patients are selected with the idea that they are best suited to provide appropriate information. Assurance that enough patients were studied to provide sufficient information should be found in the description.
Was an iterative process of collecting information used? In qualitative research, the researcher learns about the topic as the research progresses. The study design should consist of data collection and analysis, followed by more data collection and analysis, in an iterative fashion, until no more information is obtained.
Was a thorough analysis presented? A good qualitative study presents the findings and provides a thorough analysis of the data.
Are the background and training of the investigators described? Because investigators are being relied on for analysis of the data, their training and biases must be documented. These characteristics can be used to evaluate the conclusions.