Levels of Evidence in Research | Elsevier Author Services (2023)

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Evidence Hierarchy Level

While conducting a project, you may have noticed that when searching for information, different types of scientific results seem to be associated with different levels of credibility. For example, it is not the same to use a systematic review or an expert's opinion as a basis for argument. It's almost common sense that the former gives more accurate results than the latter, ultimately derived from personal opinion.

For example, in the medical and healthcare field, it is very important that professionals not only have access to information, but also have tools to determine what evidence is more solid and reliable to instill confidence to diagnose and treat their patients.

5 levels of evidence

Given the growing need for physicians, as well as scientists in different fields of study, to know what type of research to expect the best clinical evidence from, the experts decided to classify this evidence to help them identify the best sources of information to conduct research to respond to. . Your Questions The criteria for grading the evidence are based on the design, methodology, validity, and applicability of the different study types. The result is referred to as "levels of evidence" or "hierarchical levels of evidence". By organizing a well-defined hierarchy of evidence, academic experts sought to help scientists feel confident about using high-level evidence in their own work or practice. For clinicians whose daily business relies on available clinical evidence to support decision making, this really helps them to know which evidence to trust the most.

(Video) Levels of Evidence

So you know by now that research can be evaluated according to the weight of evidence determined by different study designs. But how many degrees are there? What evidence should be ranked high and low?

There are five levels of evidence in the evidence hierarchy, with 1 (or in some cases A) for strong, high-quality evidence and 5 (or E) for evidence with no proven efficacy, as you can see in the pyramid scheme below. :

Evidence Hierarchy Level

Level 1: (highest quality of evidence)– High quality randomized study or prospective study; testing previously developed diagnostic criteria in consecutive patients; costs and sensible alternatives; Values ​​from many studies with multipath sensitivity analyses; systematic review of level I RCTs and level I studies.

Level 2:lower quality RCTs; prospective comparative study; retrospective study; untreated controls from an RCT; lower quality prospective study; Development of diagnostic criteria in consecutive patients; costs and sensible alternatives; Values ​​from limited studies; with multipath sensitivity analysis; systematic review of level II studies or level I studies with conflicting results.

Level 3:case-control study (therapeutic and prognostic studies); retrospective comparative study; Study on non-consecutive patients without a consistently applied reference "gold standard"; Analysis based on alternatives and limited costs and poor estimates; systematic review of level III studies.

Level 4:case series; case-control study (diagnostic studies); poor reference standard; Analysis without sensitivity analysis.

(Video) John Hopkins EBP Model: Evidence Appraisal

Level 5: (lowest quality of evidence)- Expert Opinion.

Levels of Evidence in Research | Elsevier Author Services (1)

Using the pyramid, you can roughly distinguish which type of research gives you the highest quality of evidence and which the lowest. Basically, Level 1 and Level 2 are leaked information, meaning that an author has gathered evidence from well-designed studies with credible results and produced results and conclusions that are peer-reviewed and deemed valid and sufficiently relevant researchers and scientists. Levels 3, 4 and 5 contain evidence from unfiltered information. Because this evidence has not been peer-reviewed, it may be questionable, but not necessarily false or false.

Examples of levels of evidence

As you move up the pyramid, you are bound to find higher quality evidence. However, you will find that there is also less research available. So if you don't have resources above, you may need to move down to find the answers you're looking for.

  1. Systematic Reviews: -Exhaustive summaries of all existing literature on a given topic. When writing a systematic review, authors are expected to critically review and evaluate all of this literature and not just a simple list. Systematic review researchers have their own criteria for locating, compiling, and evaluating a collection of literature.
  2. Meta-analysis: uses quantitative methods to synthesize a combination of results from independent studies. Typically, they act as an overview of clinical trials. Continue reading:Systematic review vs. meta-analysis.
  3. Criticized topic: Evaluation of various research studies.
  4. Critically-Reviewed Article: Evaluation of Individual Research Studies.
  5. Randomized Controlled Trial: A clinical trial in which participants or subjects (people who agree to participate in the study) are randomly assigned to groups. One group will be given placebo (control) while the other will be treated with medication. This type of research is key to knowing the effectiveness of a treatment.
  6. Cohort Studies: A longitudinal study design in which one or more samples called cohorts (individuals who share a defining characteristic such as a disease) are exposed to an event and prospectively monitored and assessed at predefined time intervals. They are commonly used to correlate disease with risk factors and health outcomes.
  7. Case-Control Study: Select patients with an outcome (cases) of interest and search for an exposure factor of interest.
  8. Basic information/expert opinion: Information you can find in encyclopedias, textbooks and manuals. This type of evidence only serves as a good basis for further research or clinical practice as it is usually too general.

Of course, it is recommended to use evidence level A and/or 1 for more accurate results, but that does not mean that all other study designs are worthless or useless. It all depends on your research question. Focusing again on the health and medical space, see how the different study designs fit specific questions that aren't necessarily at the top of the pyramid:

  • Questions about therapy: "What is the most effective treatment for my patient?"
    >> RCT | Cohort Studies | case control | case studies
  • Diagnostic questions: "What diagnostic method should I use?"
    >> Prospective blind comparison
  • Prognosis questions: "How will the patient's disease develop over time?"
    >> Cohort Studies | case studies
  • Questions about etiology: "What are the causes of this disease?"
    >> RCT | Cohort Studies | case studies
  • Cost questions: "What is the most cost-effective and at the same time safest option for my patient?"
    >> Economic assessment
  • Questions about meaning/quality of life: "What will my patient's quality of life be like?"
    >> Qualitative study

All kinds of evidence are useful for the advancement of science. Whether you are writing for the top of the pyramid or its bottom, withLanguage Editing Service PlusYou can excel at writing and influence your readers in exactly the way you want them to. Our team of language experts pays special attention to the logic and flow of the content and adapts your document to your needs. In addition to professional editing, we offer reference checks and a personalized cover letter. All this, with unlimited language revision rounds and full support every step of the way. Use the simulator below to check the price of your manuscript based on the total number of words in the document.

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(Video) Evidence-Based Practice for Librarians- Levels of Evidence

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(Video) GRADE - Ch. 7 Rating the Evidence - Andy Kerwin, MD, FACS

Learn more about levels of evidence in research on Pinterest:

(Video) Creating an Evidence Table


What are the 5 levels of evidence in research? ›

Levels of Evidence
Levels of Evidence
Level IIIEvidence obtained from well-designed controlled trials without randomization (ie quasi-experimental).
Level IVEvidence from well-designed case-control or cohort studies.
Level VEvidence from systematic reviews of descriptive and qualitative studies (meta-synthesis).
4 more rows
Nov 2, 2022

How do you determine the level of evidence in a research article? ›

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."

What is the most reliable level of evidence? ›

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.

What is the weakest level of research evidence? ›

Types of Resources

(Melnyk, 2004) The weakest level of evidence is the opinion from authorities and/or reports of expert committees.

What is Step 5 in research? ›

Step 5 – Report Research Findings

The final step is to report the research findings to those who need the data to make decisions. The findings should be presented in a comprehensible format so that they can be readily used in the decision-making process.

How do you evaluate sources of evidence? ›

Common evaluation criteria include: purpose and intended audience, authority and credibility, accuracy and reliability, currency and timeliness, and objectivity or bias.
Authority and credibility
  1. Who is the author? Is it a person? ...
  2. What are the qualifications of the author? ...
  3. Who is the publisher?
Jan 18, 2023

How do you evaluate the quality of evidence of an article? ›

Assessing certainty of evidence
  1. Plan your approach to assessing certainty.
  2. Consider the importance of outcomes.
  3. Assess risk of bias (or study limitations)
  4. Assess inconsistency or heterogeneity.
  5. Assess indirectness.
  6. Assess imprecision.
  7. Assess publication biases.
  8. Consider reasons to upgrade the certainty of the evidence.
Sep 6, 2019

Why is it important to understand the type of level of evidence in a research article? ›

It is therefore important to be able to determine which evidence is the most authoritative. So-called 'levels of evidence' are used for this purpose and specify a hierarchical order for various research designs based on their internal validity (see table below).

What is the strongest evidence in research? ›

Well done systematic reviews, with or without an included meta-analysis, are generally considered to provide the best evidence for all question types as they are based on the findings of multiple studies that were identified in comprehensive, systematic literature searches.

What is the best evidence in research? ›

Best evidence includes empirical evidence from randomized controlled trials; evidence from other scientific methods such as descriptive and qualitative research; as well as use of information from case reports, scientific principles, and expert opinion.

What is the best source of evidence? ›

Evidence is published across a variety of sources, including scientific or academic journals, books, conference proceedings, websites, and news reports. Academic publications in scientific journals are generally considered to be of higher quality due to the independent, peer-review process.

What are the most reliable evidence-based sources? ›

Peer-reviewed journal articles based on research studies are your best sources of evidence-based information.

What are the rules of evidence in research? ›

There are four Rules of Evidence; Validity, Sufficiency, Authenticity and Currency. The Rules of Evidence are very closely related to the Principles of Assessment and highlight the important factors around evidence collection.

How do you find weak points in research? ›

Identifying six major weaknesses
  1. A too-broad thesis statement.
  2. A poorly formulated thesis.
  3. Inadequate or unfocused topic sentences.
  4. Writing off-subject.
  5. Failing to anticipate objections.
  6. An inadequate conclusion.

What are the 6 and 7 steps in the research process? ›

The Seven Steps of the Research Process
  1. Step 1: Identify and Develop Your Topic. ...
  2. Step 2: Find Background Information. ...
  3. Step 3: Use Catalogs to Find Books and Media. ...
  4. Step 4: Use Databases to Find Journal Articles. ...
  5. Step 5: Find Internet Resources. ...
  6. Step 6: Evaluate What You Find. ...
  7. Step 7: Cite What You Find Using a Standard Format.
Apr 14, 2022

What is Step 4 research? ›

Step 4: The Research Design

Research design is the plan for achieving objectives and answering research questions. It outlines how to get the relevant information. Its goal is to design research to test hypotheses, address the research questions, and provide decision-making insights.

What are the 4 types of research design? ›

There are four main types of Quantitative research: Descriptive, Correlational, Causal-Comparative/Quasi-Experimental, and Experimental Research. attempts to establish cause- effect relationships among the variables. These types of design are very similar to true experiments, but with some key differences.

What is the definition of levels of evidence in research? ›

Listen to pronunciation. (LEH-vulz ... EH-vih-dents) A ranking system used to describe the strength of the results measured in a clinical trial or research study.

What is the purpose of evidence in research? ›

Evidence-based research is the use of prior research in a systematic and transparent way to inform a new study so that it is answering questions that matter in a valid, efficient, and accessible manner.

What are 4 examples of evidence or proof? ›

The four types of evidence recognized by the courts include demonstrative, real, testimonial and documentary.

How do I evaluate if evidence is credible accurate and reliable? ›

To evaluate evidence for credibility, accuracy, and reliability, consider the following questions:
  1. Who/what is the source of the evidence? ...
  2. Is the evidence found in a primary or secondary source? ...
  3. How does the evidence from one source compare and contrast with the evidence from another source? ...
  4. How current is the evidence?

How do you know if a source is credible? ›

Take a closer look at the source

Does the article or study have any authors listed? If so, do they cite or link to authoritative sources, or are they writing their own opinions without backing these up with facts? Are their credentials listed? Additionally, check the date of publication.

What is the best method for evaluating evidence based practice? ›

Five Steps of the Evidence-based Process
  • Ask a clinical question.
  • Obtain the best research literature.
  • Critically appraise the evidence.
  • Integrate the evidence with clinical expertise, patient preferences.
  • Evaluate the outcomes of the decision.

What are the two keys to evaluating evidence? ›


In evaluating the evidence for an intervention, both the level of certainty of the causal relationship between the intervention and its observed outcomes and the generalizability of the evidence to other individuals, settings, contexts, and time frames should be considered.

Why it is important to present strong evidence in your claims as an author? ›

A strong thesis also requires solid evidence to support and develop it because without evidence, a claim is merely an unsubstantiated idea or opinion.

What do you think is the most important type of evidence and why? ›

Direct Evidence

The most powerful type of evidence, direct evidence requires no inference and directly proves the fact you are investigating. The evidence alone is the proof, if you believe the accounts.

What are the levels of evidence in a literature review? ›

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.

What is the most important of evidence? ›

In criminal law, physical evidence is king. Physical evidence does not have bias. Physical evidence exists independent of the hopes and wishes of anyone. This is why it is so very important for physical evidence to be discovered, not contaminated and properly analyzed.

What is the most credible source for research? ›

Credible sources include peer-reviewed journals, government agencies, research think tanks, and professional organizations. Major newspapers and magazines also provide reliable information thanks to their high publishing standards. Reputable news sources require all content to be fact-checked before publication.

What is the most reliable source for a research paper? ›

The 10 Best Academic Research Sources
  • Google Scholar.
  • JSTOR.
  • Library of Congress.
  • PubMed Central.
  • Google Books.
  • Science.gov.
  • Digital Commons Network.
  • ResearchGate.
Jul 19, 2022

What are 5 sources which are reliable academic sources? ›

What are credible sources?
  • Fact checking.
  • Sources for different purposes.
  • Dictionaries & encyclopedias.
  • Books vs scholarly books.
  • Types of journals. Peer-reviewed journals.
  • News and media.
Jul 18, 2022

What are the golden rules of evidence? ›

i) Evidence must be confined to the matter in issue. Ii) Hearsay evidence must not be admitted. Iii) Best evidence must be given in all cases.

What are the 3 requirements for evidence based practice? ›

All three elements are equally important.
  • Best Available Evidence. ...
  • Clinician's Knowledge and Skills. ...
  • Patient's Wants and Needs.

What are the three golden rules of research? ›

Three key values for ethical cyberspace research practices are evident in the articles by King and by Waskul and Douglass in this issue: (1) protect the subjects from harm as a result of the research fieldwork and the research practices; (2) produce good social science research; and (3) do not unnecessarily perturb the ...

How do you answer your weak points? ›

Answer “what is your greatest weakness” by choosing a skill that is not essential to the job you're applying to and by stressing exactly how you're practically addressing your weakness. Some skills that you can use as weaknesses include impatience, multitasking, self-criticism, and procrastination.

How do you answer strong and weak points? ›

5 tips for talking about strengths and weaknesses in an interview
  1. Be honest. ...
  2. Tell a story. ...
  3. Remember to get to the insight. ...
  4. Keep it short. ...
  5. Don't sweat it so much.
Dec 31, 2022

What is the 5 step process of conducting evidence based practice? ›

In this article, I have explained the five essential steps for practising EBM, which are: formulating answerable clinical questions; searching for evidence; making a critical appraisal; assessing the applicability of the evidence; and evaluating performance.

What is Level 6 evidence in research? ›

Level 6: Single Descriptive or Qualitative Study. Level 7: Expert Opinion. Level I Evidence. • Systematic Review or Meta-Analysis of Randomized Controlled.

What are 4 types of evidence? ›

Discussed below are the four types of evidence you should know.
  • Real Evidence. Physical evidence that is intimately linked to the case facts is called real evidence. ...
  • Testimonial Statements. Testimonial statements are sometimes called Testimonial Hearsay. ...
  • Demonstrative Evidence. ...
  • Documentary Evidence.
Oct 15, 2021

Which of the following are the 5 major parts of research *? ›

5 Major Parts of A Research Paper
  • Introduction. The introduction is the first section of a research paper, and it should provide a brief overview of the topic being studied. ...
  • Review of Literature. ...
  • Research Methods. ...
  • Results. ...
  • Discussion.
Apr 15, 2022

What are the 4 methods to incorporate evidence into academic writing? ›

Effectively Integrating Evidence
  • Writing about Evidence.
  • Attribution to a Source.
  • Verbs of Attribution.
  • Using Quotations as Evidence.
  • How to Incorporate Quotations in Paragraphs.

What are the key elements of evidence-based practice? ›

Evidence-based practice includes the integration of best available evidence, clinical expertise, and patient values and circumstances related to patient and client management, practice management, and health policy decision making. All three elements are equally important.

What are the six key characteristics of evidence-based decision making? ›

Key components of EBPH include: making decisions based on the best available scientific evidence, using data and information systems systematically, applying program planning frameworks, engaging the community in decision making, conducting sound evaluation, and disseminating what is learned.

What is Level 4 evidence in research? ›

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.

What is level U evidence? ›

Level U simply states that there is not enough evidence. We cannot say that an intervention or diagnostic modality does work, but we also cannot say that it does not work.

What does level B evidence mean? ›

B: There is fair evidence to support the recommendation that the condition be specifically considered in a periodic health examination. C: There is insufficient evidence to recommend for or against the inclusion of the condition in a periodic health examination, but recommendations may be made on other grounds.

What are the five 5 basic types of evidence? ›

The court recognizes these five types of evidence, as discussed in this piece.
  • Real evidence. Real evidence is any material that was used or present in the crime scene at the time of the crime. ...
  • Documentary evidence. ...
  • Demonstrative evidence. ...
  • Testimonial evidence. ...
  • Digital evidence.
Jul 10, 2020

What are the 3 major classification of evidence? ›

The probative value of evidence. Relevant evidence. Direct evidence. Circumstantial evidence.

What are the different types of evidence in writing? ›

There are three main categories of evidence that are essential to gain the audience's confidence in the writer's assertions. These categories are Fact, Judgment, and Testimony.

What are the 7 research components? ›

A research report has seven components:
  • Abstract or Summary.
  • Introduction.
  • Review of Literature.
  • Methods.
  • Results.
  • Conclusions and Discussion.
  • References.

What are the 6 components of research methods? ›

These components include things like your chosen: (a) research design; (b) research methodology; (c) approach within a research methodology; (d) research method(s); (e) use of longitudinal data; (f) sampling strategy; and (g) data analysis techniques.

What are the 7 steps of the research process? ›

The Seven Steps of the Research Process
  • Step 1: Identify and Develop Your Topic. ...
  • Step 2: Find Background Information. ...
  • Step 3: Use Catalogs to Find Books and Media. ...
  • Step 4: Use Databases to Find Journal Articles. ...
  • Step 5: Find Internet Resources. ...
  • Step 6: Evaluate What You Find. ...
  • Step 7: Cite What You Find Using a Standard Format.
Apr 14, 2022


1. Evidence-Based Practice, Step 2 (part II): Searching- Levels of Evidence
(ISU Libraries)
2. Critical Appraisal of Research Evidence in the Health Professions
(Carrie Price)
3. “Transitioning to Value-based Care through System-level, Evidence-based Guidelines”
(OHSU Informatics)
4. Can your causal claims be justified by evidence? | Leadership research
(Leaders' Decision Making Lab)
5. Nursing Research: Reading, Using, and Creating Evidence
(Jones & Bartlett Learning)
6. Evaluating Sources & Evidence
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