Evidence levels are currently classified by the PubMed's publication type field, only. The table below features how each publication type corresponds to an evidence level
| Name | Definition Given by the "Scope Note" column referenced here |
Evidence Level |
|---|---|---|
| Preprint | Scientific manuscript made available prior to PEER REVIEW. | 3 |
| Case Reports | Clinical presentations that may be followed by evaluative studies that eventually lead to a diagnosis. | 4 |
| Introductory Journal Article | Prefatory summary to a special issue or section of a journal devoted to a specific topic. This introductory text can be of varying length and substance. | 4 |
| Journal Article | The predominant publication type for articles and other items indexed for NLM databases. | 4 |
| Personal Narrative | Work consisting of accounts of individual experience in relation to a particular field or of participation in related activities. | 4 |
| Government Publication | Work consisting of publications issued by local, regional, or national governments or by their agencies or subdivisions. | 5 |
| Technical Report | Work consisting of a formal report giving details of the investigation and results of a medical or other scientific problem. When issued by a government agency or comparable official body, its contents may be classified, unclassified, or declassified with regard to security clearance. This publication type may also cover a scientific paper or article that records the current state or current position of scientific research and development. If so labeled by the editor or publisher, this publication type may be properly used for journal articles. | 5 |
| Clinical Study | A work that reports on the results of a research study to evaluate interventions or exposures on biomedical or health-related outcomes. The two main types of clinical studies are interventional studies (clinical trials) and observational studies. While most clinical studies concern humans, this publication type may be used for clinical veterinary articles meeting the requisites for humans. | 6 |
| Comparative Study | Comparison of outcomes, results, responses, etc for different techniques, therapeutic approaches or other inputs. | 6 |
| Evaluation Study | Works consisting of studies determining the effectiveness or utility of processes, personnel, and equipment. | 6 |
| Multicenter Study | A work that reports on a study executed by several cooperating institutions. | 6 |
| Observational Study | A work that reports on the results of a clinical study in which participants may receive diagnostic, therapeutic, or other types of interventions, but the investigator does not assign participants to specific interventions (as in an interventional study). | 6 |
| Observational Study, Veterinary | Reports on studies of the results of a clinical study in which animal subjects may receive diagnostic, therapeutic, or other types of interventions, where the investigator does not assign participants to specific interventions. | 6 |
| Twin Study | Work consisting of reporting using a method of detecting genetic causes in human traits and genetic factors in behavior using sets of twins. | 6 |
| Validation Study | Works consisting of research using processes by which the reliability and relevance of a procedure for a specific purpose are established | 6 |
| Guideline | Work consisting of a set of statements, directions, or principles presenting current or future rules or policy. Guidelines may be developed by government agencies at any level, institutions, organizations such as professional societies or governing boards, or by the convening of expert panels. The text may be cursive or in outline form, but it is generally a comprehensive guide to problems and approaches in any discipline or activity. This concept relates to the general conduct and administration of health care activities rather than to specific decisions for a particular clinical condition. For that aspect, PRACTICE GUIDELINE is available. | 7 |
| Practice Guideline | Work consisting of a set of directions or principles to assist the health care practitioner with patient care decisions about appropriate diagnostic, therapeutic, or other clinical procedures for specific clinical circumstances. Practice guidelines may be developed by government agencies at any level, institutions, organizations such as professional societies or governing boards, or by the convening of expert panels. They can provide a foundation for assessing and evaluating the quality and effectiveness of health care in terms of measuring improved health, reduction of variation in services or procedures performed, and reduction of variation in outcomes of health care delivered. | 7 |
| Review | An article or book published after examination of published material on a subject. It may be comprehensive to various degrees and the time range of material scrutinized may be broad or narrow, but the reviews most often desired are reviews of the current literature. The textual material examined may be equally broad and can encompass, in medicine specifically, clinical material as well as experimental research or case reports. State-of-the-art reviews tend to address more current matters. A review of the literature must be differentiated from HISTORICAL ARTICLE on the same subject, but a review of historical literature is also within the scope of this publication type. | 7 |
| Scientific Integrity Review | Work consisting of reports by the United States Office of Research Integrity, identifying questionable research published in articles or books. Notification of the questionable data is carried in the NIH Guide for Grants and Contracts. | 7 |
| Meta-Analysis | Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature. | 8 |
| Systematic Review | A review of primary literature in health and health policy that attempts to identify, appraise, and synthesize all the empirical evidence that meets specified eligibility criteria to answer a given research question. Its conduct uses explicit methods aimed at minimizing bias in order to produce more reliable findings regarding the effects of interventions for prevention, treatment, and rehabilitation that can be used to inform decision making. | 8 |
| Adaptive Clinical Trial | Clinical study in which a prospectively planned opportunity is included to modify trial designs and hypotheses based on analysis of data from subjects in the study. | 9 |
| Clinical Trial | A work that reports on the results of a clinical study in which participants are assigned to receive one or more interventions so that researchers can evaluate the interventions on biomedical or health-related outcomes. The assignments are determined by the study protocol. Participants may receive diagnostic, therapeutic, or other types of interventions. For clinical trials on veterinary animals see CLINICAL TRIAL, VETERINARY. Clinical Trials was used for both humans and non-humans prior to 2019. | 9 |
| Clinical Trial Protocol | The written description of a clinical study. It contains the study's objectives, design, and methods including subject target and/or enrollment criteria. It may also present relevant scientific background and statistical information. | 9 |
| Clinical Trial, Phase I | Work that is the report of a pre-planned, usually controlled, clinical study of the safety and efficacy of diagnostic, therapeutic, or prophylactic drugs, devices, or techniques based on a small number of healthy persons and conducted over the period of about a year in either the United States or a foreign country. | 9 |
| Clinical Trial, Phase II | Work that is a report of a pre-planned, usually controlled, clinical study of the safety and efficacy of diagnostic, therapeutic, or prophylactic drugs, devices, or techniques based on several hundred volunteers, including a limited number of patients, and conducted over a period of about two years in either the United States or a foreign country. | 9 |
| Clinical Trial, Phase III | Work that is a report of a pre-planned, usually controlled, clinical study of the safety and efficacy of diagnostic, therapeutic, or prophylactic drugs, devices, or techniques after phase II trials. A large enough group of patients is studied and closely monitored by physicians for adverse response to long-term exposure, over a period of about three years in either the United States or a foreign country. | 9 |
| Clinical Trial, Phase IV | Work that is a report of a planned post-marketing study of diagnostic, therapeutic, or prophylactic drugs, devices, or techniques that have been approved for general sale after clinical trials, phases I, II, and III. These studies, conducted in the United States or a foreign country, often garner additional data about the safety and efficacy of a product. | 9 |
| Clinical Trial, Veterinary | A work that is a veterinary clinical study in which animal participants are assigned to receive one or more interventions so that researchers can evaluate the interventions on biomedical or health-related outcomes. The assignments are determined by the study protocol. Animal participants may receive diagnostic, therapeutic, or other types of interventions. | 9 |
| Equivalence Trial | Trial that aims to show a new treatment is no better and no worse than the standard treatment. | 9 |
| Controlled Clinical Trial | A work that reports on a clinical trial involving one or more test treatments, at least one control treatment, specified outcome measures for evaluating the studied intervention, and a bias-free method for assigning patients to the test treatment. The treatment may be drugs, devices, or procedures studied for diagnostic, therapeutic, or prophylactic effectiveness. Control measures include placebos, active medicine, no-treatment, dosage forms and regimens, historical comparisons, etc. When randomization using mathematical techniques, such as the use of a random numbers table, is employed to assign patients to test or control treatments, the trial is characterized as a RANDOMIZED CONTROLLED TRIAL. | 10 |
| Pragmatic Clinical Trial | Randomized clinical trials that compare interventions in clinical settings and which look at a range of effectiveness outcomes and impacts. | 10 |
| Randomized Controlled Trial | A work that reports on a clinical trial that involves at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table. | 10 |
| Randomized Controlled Trial, Veterinary | A work that reports on a clinical trial with animal subjects that involves at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table. | 10 |