Describe the seven “levels of evidence” and provide an example of the type of practice change that could result from each
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Evidence-based practice (EBP) is the integration of best research evidence, clinical expertise, and patient values to inform clinical decision-making. The levels of evidence refer to a hierarchy of research designs that differ in the strength of their findings and the extent to which they are likely to produce accurate and unbiased results. In this essay, I will describe the seven levels of evidence and provide an example of the type of practice change that could result from each.
Level 1: Systematic Reviews and Meta-Analyses Systematic reviews and meta-analyses are considered the highest level of evidence. These studies use explicit and systematic methods to identify, appraise, and synthesize all the relevant research on a specific topic. The results of these studies provide a summary of the best available evidence and can guide clinical practice. For example, a systematic review and meta-analysis of randomized controlled trials on the use of probiotics for the prevention of Clostridium difficile infection in hospitalized patients concluded that probiotics were associated with a statistically significant reduction in the incidence of the infection. Based on this evidence, healthcare providers may consider the use of probiotics in their clinical practice to prevent this infection (Johnston et al., 2018).
Level 2: Randomized Controlled Trials (RCTs) RCTs are experimental studies in which participants are randomly assigned to receive either an intervention or a control condition. These studies are designed to test the effectiveness of an intervention and to minimize the effects of bias and confounding variables. For example, an RCT conducted to compare the effectiveness of cognitive-behavioral therapy (CBT) versus medication for the treatment of depression found that both interventions were equally effective in reducing symptoms of depression. Based on this evidence, healthcare providers may consider offering CBT as an alternative to medication for the treatment of depression (Cuijpers et al., 2013).
Level 3: Cohort Studies Cohort studies are observational studies in which a group of people who share a common characteristic or experience are followed over time to determine the incidence of an outcome of interest. For example, a cohort study that followed a group of smokers and non-smokers over 10 years found that the incidence of lung cancer was significantly higher in the smokers than in the non-smokers. Based on this evidence, healthcare providers may recommend smoking cessation programs to their patients to reduce their risk of lung cancer (Doll & Peto, 1976).
Level 4: Case-Control Studies Case-control studies are observational studies that compare the exposure of individuals who have a disease (cases) with the exposure of individuals who do not have the disease (controls). For example, a case-control study that compared the frequency of use of nonsteroidal anti-inflammatory drugs (NSAIDs) between patients with acute myocardial infarction (AMI) and patients without AMI found that the use of NSAIDs was associated with an increased risk of AMI. Based on this evidence, healthcare providers may advise their patients to use NSAIDs with caution and to consider alternative treatments when possible (García Rodríguez & Hernández-Díaz, 2000).
Level 5: Case Reports and Case Series Case reports and case series are descriptive studies that report on the characteristics and outcomes of individual patients. While these studies are useful in generating hypotheses and identifying rare outcomes, they are not designed to test the effectiveness of interventions. For example, a case report of a patient who developed liver injury after taking a dietary supplement containing green tea extract and catechins may prompt healthcare providers to investigate the safety of these supplements and to warn their patients of potential adverse effects (Mazzanti et al., 2009).
Level 6: Expert Opinion and Consensus Statements Expert opinion and consensus statements are based on the collective experience and judgment