Evidence-Based Practice: Understanding the Process

Katherine J. Dontje MSN, APRN, BC


Topics in Advanced Practice Nursing eJournal. 2007;7(4) 

In This Article

The Literature Review: Search Techniques

Using appropriate search techniques is an essential skill for the NP who wants to be involved in EBP.[12] One of the barriers to EBP that NPs often cite is the time it takes to search and find research evidence. Often nurses are either not familiar with how to search the literature or are overwhelmed by the amount and variety of evidence that is available.[1] There are several strategies that can be used to limit the time to find the evidence. An important part of EBP is to become familiar with resources that are available to synthesize the information such as[13]:

These resources can be accessed through most library systems; contact with a librarian facilitates finding and keeping current with the latest research evidence. The more the NP uses these resources, the easier it becomes to access evidence-based literature.

Once the literature has been searched and appropriate studies identified, the next step in the EBP Iowa Model is evaluation.[6] The research studies located need to be assessed for whether they are appropriate for utilization with the patient population in the particular clinical setting.[1] One of the controversies encountered by different disciplines related to EBP is what constitutes research evidence.

Organizations such as the Cochrane Collaborative envisioned evidence as primarily random controlled trials and systematic reviews.[10] As a discipline, nursing considers evidence from a broader perspective. According to Lang and associates, evidence refers to "research findings including random controlled trials, meta-analysis and systematic reviews, scientific expertise, patient preferences and values, existing resources and evidence-based theories."[14] The nursing perspective on EBP includes the need to value all evidence, both qualitative and quantitative, when making decisions related to patient care.

Levels of evidence. Levels of evidence provide a way to categorize the literature in terms of strength of evidence as well as methodological quality.[15] Some evidence tables only include quantitative studies with a primary emphasis on random controlled trials, while others include quantitative studies, qualitative studies, and expert opinion.

Melnyk and Fineout-Overhold[4] describe an evidence table where the level of evidence is as follows (from highest to lowest rank):

  1. Systematic review of multiple random controlled trials.

  2. Single random controlled trial.

  3. Well-designed nonrandom controlled trials.

  4. Well-designed case-control and cohort studies.

  5. Systematic reviews of descriptive and qualitative studies.

  6. Single descriptive or qualitative study.

  7. Opinion of authorities and expert committees.

The NP needs to determine, in keeping with their philosophical base, what constitutes evidence and then choose a system to rate the level of evidence in the research studies they evaluate.

Are the findings significant? The next step in evaluation of the literature is to consider if the research provides appropriate information to evaluate the research methods, techniques, and statistical findings to adequately determine if the findings are significant.[13] Many NPs find evaluation of the statistical findings the most challenging part of the EBP process. The NP needs to be familiar with epidemiologic terms and statistical measures such as:

  • Absolute risk;

  • Relative risk; and

  • Number needed to treat.

Concepts such as relative risk can indicate a relationship between 2 variables with a positive association, negative association, or no association.[16]

NPs should examine research findings and determine the level of evidence that can be attributed to the finding. The level of evidence may influence whether a finding will be incorporated into practice. In our example of depression screening a US Preventative Services Task Force (USPSTF) guideline recommends "screening adults for depression in practices where there are systems in place to assure accurate diagnosis, effective treatment and follow up."[17]

The evidence to support this recommendation comes from a variety of sources including a large number of randomized controlled trials. The USPSTF grades its recommendations on the strength of evidence and takes into consideration the benefit vs harm ratio. The scheme for strength of evidence includes 5 classifications: A, B, C, D, and I. The highest grade is A; I is an indication that there is insufficient evidence for or against a routine recommendation.

The recommendation for depression screening is classified as grade B. These recommendations were based on 192 articles included in a systematic evidence review; 70 of these were placed in an evidence table, 14 of these were randomized controlled trials. Ten of these studies examined effects of screening on depression outcomes, 5 of the 10 showed significant improvements in outcomes of depression, and 3 others showed improvement that did not reach statistical significance.

According to the USPSTF, Grade B indicates that clinicians are strongly recommended to provide the service to eligible patients. With this information, the NP should feel confident that depression screening in primary care is something that needs to be implemented in practice.


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