what level of evidence is a journal article

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Levels of Evidence / Evidence Hierarchy

Evidence pyramid (levels of evidence), definitions, research designs in the hierarchy, clinical questions --- research designs.

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Levels of evidence (sometimes called hierarchy of evidence) are assigned to studies based on the research design, quality of the study, and applicability to patient care. Higher levels of evidence have less risk of bias . 

Levels of Evidence (Melnyk & Fineout-Overholt 2023)

*Adapted from: Melnyk, & Fineout-Overholt, E. (2023).  Evidence-based practice in nursing & healthcare: A guide to best practice   (Fifth edition.). Wolters Kluwer.

" Evidence Pyramid " is a product of Tufts University and is licensed under BY-NC-SA license 4.0

Tufts' "Evidence Pyramid" is based in part on the  Oxford Centre for Evidence-Based Medicine: Levels of Evidence (2009)

Levels of Evidence (LoBiondo-Wood & Haber 2022)

Adapted from LoBiondo-Wood, G. & Haber, J. (2022). Nursing research: Methods and critical appraisal for evidence-based practice (10th ed.). Elsevier.

• Oxford Centre for Evidence Based Medicine Glossary

Different types of clinical questions are best answered by different types of research studies.  You might not always find the highest level of evidence (i.e., systematic review or meta-analysis) to answer your question. When this happens, work your way down to the next highest level of evidence.

This table suggests study designs best suited to answer each type of clinical question.

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Levels of Evidence

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Critically Appraised Individual Articles

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Grades of Recommendation

Critically-appraised individual articles and synopses include:

Filtered evidence:

• Level I: Evidence from a systematic review of all relevant randomized controlled trials.
• Level II: Evidence from a meta-analysis of all relevant randomized controlled trials.
• Level III: Evidence from evidence summaries developed from systematic reviews
• Level IV: Evidence from guidelines developed from systematic reviews
• Level V: Evidence from meta-syntheses of a group of descriptive or qualitative studies
• Level VI: Evidence from evidence summaries of individual studies
• Level VII: Evidence from one properly designed randomized controlled trial

Unfiltered evidence:

• Level VIII: Evidence from nonrandomized controlled clinical trials, nonrandomized clinical trials, cohort studies, case series, case reports, and individual qualitative studies.
• Level IX: Evidence from opinion of authorities and/or reports of expert committee

Two things to remember:

1. Studies in which randomization occurs represent a higher level of evidence than those in which subject selection is not random.

2. Controlled studies carry a higher level of evidence than those in which control groups are not used.

Strength of Recommendation Taxonomy (SORT)

• SORT The American Academy of Family Physicians uses the Strength of Recommendation Taxonomy (SORT) to label key recommendations in clinical review articles. In general, only key recommendations are given a Strength-of-Recommendation grade. Grades are assigned on the basis of the quality and consistency of available evidence.
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PHIL 201: Iverson, J. (Fall 2023): Levels of evidence & article types

• Evaluating sources: C.A.R.S.
• Levels of evidence & article types
• Finding EBP resources

What is evidence-based practice?

According the the American Association of Colleges of Nursing, evidence-based practice (EBP) is:

• Patient values and preferences
• Clinician judgment and expertise
• Using evidence to guide nursing practice

See the "Finding EBP resources" page of this tab to begin searching for EBP resources.

Levels of evidence

Levels of evidence (sometimes called hierarchy of evidence) are assigned to studies based on the methodological quality of their design, validity, and applicability to patient care. These decisions gives the grade (or strength) of recommendation.

Adapted from: Melnyk, B.M. & Fineout-Overholt, E. (2011). Evidence-based practice in nursing and healthcare: A guide to best practice. Philadelphia: Lippincott, Williams & Wilkins.

Filtered versus unfiltered resources

Filtered sources.

As unfiltered or primary literature begins to circulate, others who were usually not involved in the original research, provide analysis, interpretation, and often synthesis of the primary literature, either of individual studies or groups of them. This is the secondary, or filtered literature. It can take the form of review articles, systematic reviews, meta-analyses, evidence summaries, or guidelines.

Unfiltered sources

The reporting and dissemination of scientific research follows a cycle. Reports of new, original research written by the scientists who conducted it are sometimes referred to as primary, or unfiltered literature. These first-hand accounts can take the form of journal articles, conference proceedings, dissertations, technical reports, or more informal online communications.

Regardless of what type of literature you're consulting, be critical! (See the Evaluating sources subpage under the "Appropriate?" tab above for more information).

How to read and critique an empirical research article

Article types

Empirical research articles.

Empirical research articles are reports of original scientific research, written by the scientists themselves. They can be identified by having some or all of the following characteristics:

• Multiple authors (usually at least 3)
• Can be quite lengthy, depending on the journal (10+ pages)
• Long, technical titles
• Thick in the language of the speciality, lots of jargon
• Include an abstract
• Divided into sections, which often include “Objectives”, “Methods”, “Discussion”, and “Results”
• Charts, graphs, and tables
• Lengthy references list

These are unfiltered or primary resources. These can be levels 2-4 or 6 depending on the methods used.

Literature Reviews

Literature reviews are meant to analyze and pull together – in one place -- the results of different research projects on a specific topic. They are usually written by a scholar/practitioner in the field, but not necessarily by someone who has done empirical research themselves. Literature review articles can be identified by having some or all of the following characteristics:

• Usually just one, or maybe two, authors
• Often brief, two or three pages
• Titles are not necessarily technical-sounding, and may even include the word “review” in them
• Peppered with references to other research

These are filtered or secondary resources. These are level 7 , as the literature is typically reviewed in a nonsystematic, idiosyncratic way and conclusions can be more opinion based rather than evidence based.

Systematic Reviews

Systematic reviews are literature reviews focused on a single question that try to identify, appraise, select and synthesize all high quality research evidence relevant to that question. 

• Systematic reviews use explicit methods to identify, select, and critically evaluate relevant research.
• Systematic reviews minimize the possibility of bias by using explicit criteria, and expand the relevance of individual studies with limited scope, but ...
• Only a small number of clinical topics are covered by systematic reviews, because they require years of effort to develop.

These are filtered or secondary resources. These are level 1 , unless focusing on descriptive or qualitative studies (in which case they are level 5)

Meta-analyses

Meta-analyses are systematic reviews that combine the results of several studies (often clinical trials) using quantitative statistics. They may be used to evaluate therapeutic effectiveness, plan new studies, etc.

These are filtered or secondary resources. These are level 1 .

Clinical Practice Guidelines

Clinical practice guidelines are systematically developed statements of appropriate care designed to assist the practitioner and patient make decisions about appropriate health care for specific clinical circumstances.

• Guidelines from reputable, authoritative organizations are usually based on the most current, relevant research, but ...
• Guidelines are developed using widely varying standards. Cost may be considered as well as health outcomes
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How do i determine the level of evidence of an article, johns hopkins nursing ebp: levels of evidence.

Level I Experimental study, randomized controlled trial (RCT) Systematic review of RCTs, with or without meta-analysis

Level II Quasi-experimental Study Systematic review of a combination of RCTs and quasi-experimental, or quasi-experimental studies only, with or without meta-analysis.

Level III Non-experimental study Systematic review of a combination of RCTs, quasi-experimental and non-experimental, or non-experimental studies only, with or without meta-analysis. Qualitative study or systematic review, with or without meta-analysis

Level IV Opinion of respected authorities and/or nationally recognized expert committees/consensus panels based on scientific evidence.     Includes:          - Clinical practice guidelines          - Consensus panels

Level V Based on experiential and non-research evidence.     Includes:       - Literature reviews       - Quality improvement, program or financial evaluation       - Case reports       - Opinion of nationally recognized expert(s) based on experiential evidence

From   Johns   Hopkins   nursing  evidence-based practice : Models and Guidelines Dearholt, S., Dang, Deborah, & Sigma Theta Tau International. (2012).  Johns Hopkins Nursing Evidence-based Practice : Models and Guidelines .

The links below will provide further information. 

Links & Files

• The JBI Levels of Evidence
• Tutorial - Identifying Types of Evidence
• Tutorial - Using the Hierarchy of Evidence
• Tutorial - Understanding Study Design
• Winona State University Level of Evidence page
• Last Updated Jan 11, 2022
• Answered By Anne Heimann

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What are the levels of evidence?

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"Levels of Evidence" are often represented in as a pyramid, with the highest level of evidence at the top:

"Levels of Evidence" tables have been developed which outline and grade the best evidence. However, the review question will determine the choice of study design.

Secondary sources provide analysis, synthesis, interpretation and evaluation of primary works. Secondary sources are not evidence, but rather provide a commentary on and discussion of evidence. e.g. systematic review

Primary sources contain the original data and analysis from research studies. No outside evaluation or interpretation is provided. An example of a primary literature source is a peer-reviewed research article. Other primary sources include preprints, theses, reports and conference proceedings.

Levels of evidence for primary sources fall into the following broad categories of study designs   (listed from highest to lowest):

• Experimental : RTC's (Randomised Control Trials)
• Quasi-experimental studies (Non-randomised control studies, Before-and-after study, Interrupted time series)
• Observational studies (Cohort study, Case-control study, Case series) 

Based on information from Centre for Reviews and Dissemination. (2009). Systematic reviews: CRD's guidance for undertaking reviews in health care. Retrieved from http://www.york.ac.uk/inst/crd/index_guidance.htm

Image from : Evidence-Based Practice in the Health Sciences: Evidence-Based Nursing Tutorial Information Services Department of the Library of the Health Sciences-Chicago , University of Illinois at Chicago. Contact lib-cref {at}uic.edu | Creative Commons licence

The following definitions are from the Glossary from the  Centre for Evidence Based Medicine  (CEBM), University of Oxford: 

• Systematic Review An article in which the authors have systematically searched for, appraised, and summarised all of the medical literature for a specific topic.
• Critically appraised topic A short summary of an article from the literature, created to answer a specific clinical question.
• Randomised controlled clinical trial A group of patients is randomised into an experimental group and a control group. These groups are followed up for the variables/outcomes of interest.
• Cohort study Involves the identification of two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
• Case-control study Involves identifying patients who have the outcome of interest (cases) and control patients without the same outcome, and looking to see if they had the exposure of interest.
• Meta-analysis: A systematic review which uses quantitative methods to summarise the results
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• Research Process

Levels of evidence in research

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Table of Contents

Level of evidence hierarchy

When carrying out a project you might have noticed that while searching for information, there seems to be different levels of credibility given to different types of scientific results. For example, it is not the same to use a systematic review or an expert opinion as a basis for an argument. It’s almost common sense that the first will demonstrate more accurate results than the latter, which ultimately derives from a personal opinion.

In the medical and health care area, for example, it is very important that professionals not only have access to information but also have instruments to determine which evidence is stronger and more trustworthy, building up the confidence to diagnose and treat their patients.

5 levels of evidence

With the increasing need from physicians – as well as scientists of different fields of study-, to know from which kind of research they can expect the best clinical evidence, experts decided to rank this evidence to help them identify the best sources of information to answer their questions. The criteria for ranking evidence is based on the design, methodology, validity and applicability of the different types of studies. The outcome is called “levels of evidence” or “levels of evidence hierarchy”. By organizing a well-defined hierarchy of evidence, academia experts were aiming to help scientists feel confident in using findings from high-ranked evidence in their own work or practice. For Physicians, whose daily activity depends on available clinical evidence to support decision-making, this really helps them to know which evidence to trust the most.

So, by now you know that research can be graded according to the evidential strength determined by different study designs. But how many grades are there? Which evidence should be high-ranked and low-ranked?

There are five levels of evidence in the hierarchy of evidence – being 1 (or in some cases A) for strong and high-quality evidence and 5 (or E) for evidence with effectiveness not established, as you can see in the pyramidal scheme below:

Level 1: (higher quality of evidence) – High-quality randomized trial or prospective study; testing of previously developed diagnostic criteria on consecutive patients; sensible costs and alternatives; values obtained from many studies with multiway sensitivity analyses; systematic review of Level I RCTs and Level I studies.

Level 2: Lesser quality RCT; prospective comparative study; retrospective study; untreated controls from an RCT; lesser quality prospective study; development of diagnostic criteria on consecutive patients; sensible costs and alternatives; values obtained from limited stud- ies; with multiway sensitivity analyses; systematic review of Level II studies or Level I studies with inconsistent results.

Level 3: Case-control study (therapeutic and prognostic studies); retrospective comparative study; study of nonconsecutive patients without consistently applied reference “gold” standard; analyses based on limited alternatives and costs and poor estimates; systematic review of Level III studies.

Level 4: Case series; case-control study (diagnostic studies); poor reference standard; analyses with no sensitivity analyses.

Level 5: (lower quality of evidence) – Expert opinion.

By looking at the pyramid, you can roughly distinguish what type of research gives you the highest quality of evidence and which gives you the lowest. Basically, level 1 and level 2 are filtered information – that means an author has gathered evidence from well-designed studies, with credible results, and has produced findings and conclusions appraised by renowned experts, who consider them valid and strong enough to serve researchers and scientists. Levels 3, 4 and 5 include evidence coming from unfiltered information. Because this evidence hasn’t been appraised by experts, it might be questionable, but not necessarily false or wrong.

Examples of levels of evidence

As you move up the pyramid, you will surely find higher-quality evidence. However, you will notice there is also less research available. So, if there are no resources for you available at the top, you may have to start moving down in order to find the answers you are looking for.

• Systematic Reviews: -Exhaustive summaries of all the existent literature about a certain topic. When drafting a systematic review, authors are expected to deliver a critical assessment and evaluation of all this literature rather than a simple list. Researchers that produce systematic reviews have their own criteria to locate, assemble and evaluate a body of literature.
• Meta-Analysis: Uses quantitative methods to synthesize a combination of results from independent studies. Normally, they function as an overview of clinical trials. Read more: Systematic review vs meta-analysis .
• Critically Appraised Topic: Evaluation of several research studies.
• Critically Appraised Article: Evaluation of individual research studies.
• Randomized Controlled Trial: a clinical trial in which participants or subjects (people that agree to participate in the trial) are randomly divided into groups. Placebo (control) is given to one of the groups whereas the other is treated with medication. This kind of research is key to learning about a treatment’s effectiveness.
• Cohort studies: A longitudinal study design, in which one or more samples called cohorts (individuals sharing a defining characteristic, like a disease) are exposed to an event and monitored prospectively and evaluated in predefined time intervals. They are commonly used to correlate diseases with risk factors and health outcomes.
• Case-Control Study: Selects patients with an outcome of interest (cases) and looks for an exposure factor of interest.
• Background Information/Expert Opinion: Information you can find in encyclopedias, textbooks and handbooks. This kind of evidence just serves as a good foundation for further research – or clinical practice – for it is usually too generalized.

Of course, it is recommended to use level A and/or 1 evidence for more accurate results but that doesn’t mean that all other study designs are unhelpful or useless. It all depends on your research question. Focusing once more on the healthcare and medical field, see how different study designs fit into particular questions, that are not necessarily located at the tip of the pyramid:

• Questions concerning therapy: “Which is the most efficient treatment for my patient?” >> RCT | Cohort studies | Case-Control | Case Studies
• Questions concerning diagnosis: “Which diagnose method should I use?” >> Prospective blind comparison
• Questions concerning prognosis: “How will the patient’s disease will develop over time?” >> Cohort Studies | Case Studies
• Questions concerning etiology: “What are the causes for this disease?” >> RCT | Cohort Studies | Case Studies
• Questions concerning costs: “What is the most cost-effective but safe option for my patient?” >> Economic evaluation
• Questions concerning meaning/quality of life: “What’s the quality of life of my patient going to be like?” >> Qualitative study

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The Levels of Evidence and their role in Evidence-Based Medicine

Patricia b. burns.

1 Research Associate, Section of Plastic Surgery, Department of Surgery, The University of Michigan Health System

Rod J. Rohrich

2 Professor of Surgery, Department of Plastic Surgery, University of Texas Southwestern Medical Center

Kevin C. Chung

3 Professor of Surgery, Section of Plastic Surgery, Department of Surgery, The University of Michigan Health System

As the name suggests, evidence-based medicine (EBM), is about finding evidence and using that evidence to make clinical decisions. A cornerstone of EBM is the hierarchical system of classifying evidence. This hierarchy is known as the levels of evidence. Physicians are encouraged to find the highest level of evidence to answer clinical questions. Several papers published in Plastic Surgery journals concerning EBM topics have touched on this subject. 1 – 6 Specifically, previous papers have discussed the lack of higher level evidence in PRS and need to improve the evidence published in the journal. Before that can be accomplished, it is important to understand the history behind the levels and how they should be interpreted. This paper will focus on the origin of levels of evidence, their relevance to the EBM movement and the implications for the field of plastic surgery as well as the everyday practice of plastic surgery.

History of Levels of Evidence

The levels of evidence were originally described in a report by the Canadian Task Force on the Periodic Health Examination in 1979. 7 The report’s purpose was to develop recommendations on the periodic health exam and base those recommendations on evidence in the medical literature. The authors developed a system of rating evidence ( Table 1 ) when determining the effectiveness of a particular intervention. The evidence was taken into account when grading recommendations. For example, a Grade A recommendation was given if there was good evidence to support a recommendation that a condition be included in the periodic health exam. The levels of evidence were further described and expanded by Sackett 8 in an article on levels of evidence for antithrombotic agents in 1989 ( Table 2 ). Both systems place randomized controlled trials (RCT) at the highest level and case series or expert opinions at the lowest level. The hierarchies rank studies according to the probability of bias. RCTs are given the highest level because they are designed to be unbiased and have less risk of systematic errors. For example, by randomly allocating subjects to two or more treatment groups, these types of studies also randomize confounding factors that may bias results. A case series or expert opinion is often biased by the author’s experience or opinions and there is no control of confounding factors.

Canadian Task Force on the Periodic Health Examination’s Levels of Evidence *

Levels of Evidence from Sackett *

Modification of levels

Since the introduction of levels of evidence, several other organizations and journals have adopted variation of the classification system. Diverse specialties are often asking different questions and it was recognized that the type and level of evidence needed to be modified accordingly. Research questions are divided into the categories: treatment, prognosis, diagnosis, and economic/decision analysis. For example, Table 3 shows the levels of evidence developed by the American Society of Plastic Surgeons (ASPS) for prognosis 9 and Table 4 shows the levels developed by the Centre for Evidence Based Medicine (CEBM) for treatment. 10 The two tables highlight the types of studies that are appropriate for the question (prognosis versus treatment) and how quality of data is taken into account when assigning a level. For example, RCTs are not appropriate when looking at the prognosis of a disease. The question in this instance is: “What will happen if we do nothing at all”? Because a prognosis question does not involve comparing treatments, the highest evidence would come from a cohort study or a systematic review of cohort studies. The levels of evidence also take into account the quality of the data. For example, in the chart from CEBM, poorly designed RCTs have the same level of evidence as a cohort study.

Levels of Evidence for Prognostic Studies *

Levels of Evidence for Therapeutic Studies *

A grading system that provides strength of recommendations based on evidence has also changed over time. Table 5 shows the Grade Practice Recommendations developed by ASPS. The grading system provides an important component in evidence-based medicine and assists in clinical decision making. For example, a strong recommendation is given when there is level I evidence and consistent evidence from Level II, III and IV studies available. The grading system does not degrade lower level evidence when deciding recommendations if the results are consistent.

Grade Practice Recommendations *

Interpretation of levels

Many journals assign a level to the papers they publish and authors often assign a level when submitting an abstract to conference proceedings. This allows the reader to know the level of evidence of the research but the designated level of evidence does always guarantee the quality of the research. It is important that readers not assume that level 1 evidence is always the best choice or appropriate for the research question. This concept will be very important for all of us to understand as we evolve into the field of EBM in Plastic Surgery. By design, our designated surgical specialty will always have important articles that may have a lower level of evidence due to the level of innovation and technique articles which are needed to move our surgical specialty forward.

Although RCTs are the often assigned the highest level of evidence, not all RCTs are conducted properly and the results should be carefully scrutinized. Sackett 8 stressed the importance of estimating types of errors and the power of studies when interpreting results from RCTs. For example, a poorly conducted RCT may report a negative result due to low power when in fact a real difference exists between treatment groups. Scales such as the Jadad scale have been developed to judge the quality of RCTs. 11 Although physicians may not have the time or inclination to use a scale to assess quality, there are some basic items that should be taken into account. Items used for assessing RCTs include: randomization, blinding, a description of the randomization and blinding process, description of the number of subjects who withdrew or drop out of the study; the confidence intervals around study estimates; and a description of the power analysis. For example, Bhandari et al. 12 published a paper assessing the quality of surgical RCTs. The authors evaluated the quality of RCTs reported in the Journal of Bone and Joint Surgery (JBJS) from 1988–2000. Papers with a score of > 75% were deemed high quality and 60% of the papers had a score < 75%. The authors identified 72 RCTs during this time period and the mean score was 68%. The main reason for the low quality score was lack of appropriate randomization, blinding, and a description of patient exclusion criteria. Another paper found the same quality score of papers in JBJS with a level 1 rating compared to level 2. 13 Therefore, one should not assume that level 1 studies have higher quality than level 2.

A resource for surgeons when appraising levels of evidence are the users’ guides published in the Canadian Journal of Surgery 14 , 15 and the Journal of Bone and Joint Surgery. 16 Similar papers that are not specific to surgery have been published in the Journal of the American Medical Association (JAMA). 17 , 18

Plastic surgery and EBM

The field of plastic surgery has been slow to adopt evidence-based medicine. This was demonstrated in a paper examining the level of evidence of papers published in PRS. 19 The authors assigned levels of evidence to papers published in PRS over a 20 year period. The majority of studies (93% in 1983) were level 4 or 5, which denotes case series and case reports. Although the results are disappointing, there was some improvement over time. By 2003 there were more level 1studies (1.5%) and fewer level 4 and 5 studies (87%). A recent analysis looked at the number of level 1 studies in 5 different plastic surgery journals from 1978–2009. The authors defined level 1 studies as RCTs and meta-analysis and restricted their search to these studies. The number of level 1 studies increased from 1 in 1978 to 32 by 2009. 20 From these results, we see that the field of plastic surgery is improving the level of evidence but still has a way to go, especially in improving the quality of studies published. For example, approximately a third of the studies involved double blinding, but the majority did not randomize subjects, describe the randomization process, or perform a power analysis. Power analysis is another area of concern in plastic surgery. A review of the plastic surgery literature found that the majority of published studies have inadequate power to detect moderate to large differences between treatment groups. 21 No matter what the level of evidence for a study, if it is under powered, the interpretation of results is questionable.

Although the goal is to improve the overall level of evidence in plastic surgery, this does not mean that all lower level evidence should be discarded. Case series and case reports are important for hypothesis generation and can lead to more controlled studies. Additionally, in the face of overwhelming evidence to support a treatment, such as the use of antibiotics for wound infections, there is no need for an RCT.

Clinical examples using levels of evidence

In order to understand how the levels of evidence work and aid the reader in interpreting levels, we provide some examples from the plastic surgery literature. The examples also show the peril of medical decisions based on results from case reports.

An association was hypothesized between lymphoma and silicone breast implants based on case reports. 22 – 27 The level of evidence for case reports, depending on the scale used, is 4 or 5. These case reports were used to generate the hypothesis that a possible association existed. Because of these results, several large retrospective cohort studies from the United States, Canada, Denmark, Sweden and Finland were conducted. 28 – 32 The level of evidence for a retrospective cohort is 2. All of these studies had many years of follow-up for a large number of patients. Some of the studies found an elevated risk and others no risk for lymphoma. None of the studies reached statistical significance. Therefore, higher level evidence from cohort studies does not provide evidence of any risk of lymphoma. Finally, a systematic review was performed that combined the evidence from the retrospective cohorts. 27 The results found an overall standardized incidence ratio of 0.89 (95% CI 0.67–1.18). Because the confidence intervals include 1, the results indicate there is no increased incidence. The level of evidence for the systematic review is 1. Based on the best available evidence, there is no association between lymphoma and silicone implants. This example shows how low level evidence studies were used to generate a hypothesis, which then led to higher level evidence that disproved the hypothesis. This example also demonstrates that RCTs are not feasible for rare events such as cancer and the importance of observational studies for a specific study question. A case-control study is a better option and provides higher evidence for testing the prognosis of the long-term effect of silicone breast implants.

Another example is the injection of epinephrine in fingers. Based on case reports prior to 1950, physicians were advised that epinephrine injection can result in finger ischemia. 33 We see in this example in which level 4 or 5 evidence was accepted as fact and incorporated into medical textbooks and teaching. However, not all physicians accepted this evidence and are performing injections of epinephrine into the fingers with no adverse effects on the hand. Obviously, it was time for higher level evidence to resolve this issue. An in-depth review of the literature from 1880 to 2000 by Denkler, 33 identified 48 cases of digital infarction of which 21 were injected with epinephrine. Further analysis found that the addition of procaine to the epinephrine injection was the cause of the ischemia. 34 The procaine used in these injections included toxic acidic batches that were recalled in 1948. In addition, several cohort studies found no complications from the use of epinephrine in the fingers and hand. 35 , 36 , 37 The results from these cohort studies increased the level of evidence. Based on the best available evidence from these studies, the hypothesis that epinephrine injection will harm fingers was rejected. This example highlights the biases inherent in case reports. It also shows the risk when spurious evidence is handed down and integrated into medical teaching.

Obtaining the best evidence

We have established the need for RCTs to improve evidence in plastic surgery but have also acknowledged the difficulties, particularly with randomization and blinding. Although RCTs may not be appropriate for many surgical questions, well designed and conducted cohort or case-control studies could boost the level of evidence. Many of the current studies tend to be descriptive and lack a control group. The way forward seems clear. Plastic surgery researchers need to consider utilizing a cohort or case-control design whenever an RCT is not possible. If designed properly, the level of evidence for observational studies can approach or surpass those from an RCT. In some instances, observation studies and RCTs have found similar results. 38 If enough cohort or case-control studies become available, this increases the prospect of systematic reviews of these studies that will increase overall evidence levels in plastic surgery.

The levels of evidence are an important component of EBM. Understanding the levels and why they are assigned to publications and abstracts helps the reader to prioritize information. This is not to say that all level 4 evidence should be ignored and all level 1 evidence accepted as fact. The levels of evidence provide a guide and the reader needs to be cautious when interpreting these results.

Acknowledgments

Supported in part by a Midcareer Investigator Award in Patient-Oriented Research (K24 AR053120) from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (to Dr. Kevin C. Chung).

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

NS6140: Navigating Information Resources: 3. Levels of evidence, article types, & reporting requirements

• 1. How to develop a PubMed search strategy
• 2. PubMed tutorials
• 3. Levels of evidence, article types, & reporting requirements
• 4. Reading a scientific paper
• 5. Managing citations & creating a bibliography

Evidence based medicine is "the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients." 

Source: David Sackett, William Rosenberg, Muir Gray, Brian Haynes & Scott Richardson. Evidence based medicine: what it is and what it isn’t [internet]. BMJ; 13 January 1996 [cited 23 May 2013]. Available from:  http://www.bmj.com/content/312/7023/71

Levels of evidence by study type

Level I - Evidence from a systematic review or meta-analysis of all relevant randomized controlled trials (RCTs)

Level II - Evidence obtained from well-designed RCTs

Level III - Evidence obtained from well-designed controlled trials without randomization

Level IV - Evidence from well-designed case-control and cohort studies

Level V - Evidence from systematic reviews of descriptive and qualitative studies

Level VI - Evidence from single descriptive or qualitative studies

Level VII - Evidence from the opinion of authorities and/or reports of expert committees

Source: Melnyk BM.  Implementing the Evidence-Based Practice (EBP) Competencies in Healthcare : A Practical Guide to Improving Quality, Safety, and Outcomes.  ; 2016. (Table 1.1, p. 11)

Article types explained

Empirical study (or primary article):  

• Aims to gain new knowledge on a topic through direct or indirect observation and research. 
• Include quantitative or qualitative data and analysis.
• In science, an empirical article will often include the following sections: Introduction, Methods, Results, and Discussion.

Review article:  

• Provides a synthesis of existing research on a particular topic. 
• Useful when you want to get an idea of a body of research that you are not yet familiar with. 
• Differs from a systematic review in that it does not aim to capture ALL of the research on a particular topic.

Systematic review:  

• A methodical and thorough literature review focused on a particular research question. 
• Aims to identify and synthesize all of the scholarly research on a particular topic in an unbiased, reproducible way to provide evidence for practice and policy-making. 
• May involve a meta-analysis (see below). 

Meta-analysis:   

• A type of research study that combines or contrasts data from different independent studies in a new analysis in order to strengthen the understanding of a particular topic. 
• There are many methods, some complex, applied to performing this type of analysis.

Study design resources and reporting requirements 

• Study Designs 101: a tutorial from Himmelfarb Health Sciences Library at George Washington University

CONSORT Statement   is an evidence-based, minimum set of recommendations for reporting randomized trials. It offers a standard way for authors to prepare reports of trial findings, facilitating their complete and transparent reporting, and aiding their critical appraisal and interpretation.

The PRISMA Checklist is list of Preferred Reporting Items for Systematic reviews and Meta-analyses

STROBE checklists aim to STrengthen the Reporting of Observational Studies in Epidemiology

The Rubik's Cube is the most popular puzzle toy. Read the beginner's solution guide to learn how to solve it easily.

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Evidence-Based Practice for Health Professionals

• Levels of Evidence
• What is EBP?
• Asking Your Question

Types of Resources

Study design, understanding preprints & author manuscripts.

• EBP Glossaries
• Evidence Appraisal

For individual research help, schedule an appointment to meet with a librarian.

When searching for evidence-based information, one should select the highest level of evidence possible--systematic reviews or meta-analysis. Systematic reviews, meta-analysis, and critically-appraised topics/articles have all gone through an evaluation process: they have been "filtered". 

Information that has not been critically appraised is considered "unfiltered".

As you move up the pyramid, however, fewer studies are available; it's important to recognize that high levels of evidence may not exist for your clinical question.  If this is the case, you'll need to move down the pyramid if your quest for resources at the top of the pyramid is unsuccessful.

Image Credit: Glover, Jan; Izzo, David; Odato, Karen & Lei Wang.  EBM Pyramid . Dartmouth University/Yale University. 2006.

• Meta-Analysis:  A systematic review that uses quantitative methods to summarize the results.
• Systematic Review:  An article in which the authors have systematically searched for, appraised, and summarised all of the medical literature for a specific topic.
• Critically Appraised Topic : Authors of critically-appraised topics evaluate and synthesize multiple research studies.
• Critically Appraised Articles:  Authors of critically-appraised individual articles evaluate and synopsize individual research studies.
• Randomized Controlled Trials:  RCT's include a randomized group of patients in an experimental group and a control group. These groups are followed up for the variables/outcomes of interest.
• Cohort Study:  Identifies two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
• Case-Control Study:  Involves identifying patients who have the outcome of interest (cases) and control patients without the same outcome, and looking to see if they had the exposure of interest.
• Background Information/Expert Opinion:  Handbooks, encyclopedias, and textbooks often provide a good foundation or introduction and often include generalized information about a condition.  While background information presents a convenient summary, often it takes about three years for this type of literature to be published.
• Animal Research / Lab Studies:  Information begins at the bottom of the pyramid: this is where ideas and laboratory research takes place. Ideas turn into therapies and diagnostic tools, which then are tested with lab models and animals.

Different types of clinical questions are best answered by different types of research studies.  You might not always find the highest level of evidence (i.e., systematic review or meta-analysis) to answer your question. When this happens, work your way down the Evidence Pyramid to the next highest level of evidence.

This table suggests study designs best suited to answer each type of clinical question.

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• URL: https://libguides.nvcc.edu/evidence-based-practice