Evidence-Based Practice

After creating your PICO question, your next step is finding answers in the literature.  We are going to call this evidence.  There are two search strategies that are effective for finding evidence:

• Based on PICO question
• Based on the type of evidence needed

• Meta-Analysis

  A thorough examination of a number of valid studies on a topic with results combined using standard statistical methodology, as if they were from one large study.

• Systematic Reviews

  Focus is on a clinical topic and an answer to a specific question. Multiple studies are reviewed and assessed.  The results are summarized according to the predetermined criteria of the review question.

• Randomized Control Trials (RCTs)

  An experimental project that studies the effect of a therapy on real patients. Methodologies used reduce the potential for bias (randomization and blinding) and allow for comparison between intervention groups and control groups.

• Cross Sectional Studies

  Describe the relationship between diseases and other factors at one point in time in a defined population. Cross sectional studies lack any information on timing of exposure and outcome relationships and include only prevalent cases. They are often used for comparing diagnostic tests.

• Prospective, Blind Comparisons to Gold Standard

  Studies that show the efficacy of a diagnostic test. This is a controlled trial that looks at patients with varying degrees of an illness and administers both diagnostic tests (the test under investigation and the “gold standard” test) to all patients in the study group.

• Cohort Studies

  Takes a large population and follows, over time, patients with a specific condition or treatment; this group is compared with another group that has not been affected by the condition or treatment being studied. Cohort studies are observational and not as reliable as RCTs, since the two groups may differ in ways other than in the variable under study.

• Case Control Studies

  Patients who already have a specific condition are compared with people who do not. Medical records and patient recall are often used for data collection. Case control studies are less reliable than RCTs and cohort studies because showing a statistical relationship does not mean that one factor necessarily caused the other.

• Case Series & Case Reports

  Collections of reports on the treatment of individual patients or a report on a single patient. They have no statistical validity because they use no control groups and cannot compare outcomes.

There are three main categories of information. Filtered information is the highest quality, background information is the lowest.

• Background information

  Provides broad overviews of medical topics, which help increase your understanding of the topics and acquaint you with the related evidence-based literature. Types of resources include information found in clinical reference books, reference websites, practice guidelines, and consensus statements.

• Unfiltered information

  Consists of original research that has not been critically reviewed. These resources have the most current information, but you have to consider their validity and applicability. Types of resources include primary source journal articles, RCTs, cohort studies, case-controlled studies, and case series/reports.

• Filtered information

  Reviews of original research that appraise the quality of studies and make recommendations for practice. Types of resources include systematic reviews, meta-analyses, and critically appraised topics and articles.

Remember that the type of PICO question usually determines the study design.  This is a brief review of some common types of questions:

Therapy: Which treatment is the most effective, or what is an effective treatment for a particular condition

Diagnosis: How to select a diagnostic test or how to interpret the results of a particular test

Prognosis: What is the patient's likely course of disease, or how to screen for or reduce risk

Harm/Etiology: Are there harmful effects of a particular treatment, or how these harmful effects can be avoided

Prevention: How can the patient's risk factors be adjusted to help reduce the risk of disease

For a more detailed list of questions, go the "Designing PICO Questions" page under "Types of Questions.

Now that you have an idea of what type of question you are asking, use the chart below to see what study designs work best:

*Meta-analyses and systematic reviews are not appropriate for every assignment.  If your assignment is to write a review of the current literature, you should not include a meta-analysis or systematic review unless it is for background information only (i.e. not one of your reviewed articles).