PhysicsWiki:Identifying reliable sources (medicine)

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PhysicsWiki's articles, while not intended to provide medical advice, are nonetheless an important and widely used source of health information.[1] Therefore, it is vital that the biomedical information in all types of articles be based on reliable, third-party, published secondary sources and accurately reflect current medical knowledge.

Ideal sources for biomedical content includes literature reviews or systematic reviews published in reputable medical journals, academic and professional books written by experts in the relevant field and from a respected publisher, and medical guidelines or position statements from nationally or internationally recognised expert bodies. Primary sources should generally not be used for medical content. Many such sources represent unreliable information that has not been vetted in review articles, or present preliminary information that may not bear out when tested in clinical trials.

This guideline supports the general sourcing policy at PhysicsWiki:Verifiability with specific attention given to sources appropriate for the medical and health-related content in any type of article, including alternative medicine. Sources for all other types of content—including all non-medical information in medicine-related articles—are covered by the general guideline on identifying reliable sources rather than this specific guideline.

See the reliable sources noticeboard for queries about the reliability of particular sources or ask at relevant WikiProjects such as WikiProject Medicine and WikiProject Pharmacology.


  • A primary source in medicine is one in which the authors directly participated in the research or documented their personal experiences. They examined the patients, injected the rats, filled the test tubes, or at least supervised those who did. Many, but not all, papers published in medical journals are primary sources for facts about the research and discoveries made.
  • A secondary source in medicine summarizes one or more primary or secondary sources, usually to provide an overview of the current understanding of a medical topic, to make recommendations, or to combine the results of several studies. Examples include literature reviews or systematic reviews found in medical journals, specialist academic or professional books, and medical guidelines or position statements published by major health organizations.
  • A tertiary source usually summarizes a range of secondary sources. Undergraduate textbooks, lay scientific books, and encyclopedias are examples of tertiary sources.

All PhysicsWiki articles should be based on reliable, published secondary sources. Primary sources should generally not be used for health-related content, because the primary biomedical literature is exploratory and not reliable - any given primary source may be contradicted by another, and the PhysicsWiki community relies on the guidance of expert reviews, and statements of major medical and scientific bodies, to provide guidance on any given issue. The rare edits that rely on primary sources should have minimal PW:WEIGHT, should only describe the conclusions of the source, and should describe these findings clearly so the edit can be checked by editors with no specialist knowledge. In the rare cases when they are used, primary sources should not be cited in support of a conclusion that is not clearly made by the authors (see: PhysicsWiki:No original research).

Basic advice

Respect secondary sources

Individual primary sources should not be cited or juxtaposed so as to "debunk", contradict, or counter the conclusions of reliable secondary sources. Synthesis of published material that advances a position is a form of original research and should be avoided in PhysicsWiki articles, which are not a venue for open research. Controversies or areas of uncertainty in medicine should be illustrated with reliable secondary sources describing the varying viewpoints. Primary sources favoring a minority opinion should not be aggregated or presented devoid of context in such a way as to undermine proportionate representation of expert opinion in a field as presented in secondary sources. If the same material could be supported by either a primary source or a secondary source, the secondary source should be cited. A primary source may be presented adjunctively to a secondary source.

Scientific findings are often touted in the popular press as soon as the original, primary research report is released, and before the scientific community has had an opportunity to analyze the new results. Such sources should generally be entirely omitted (in accordance with recentism), because determining the weight to give to such a study requires reliable secondary sources (not press releases or newspaper articles based on them). If the conclusions of the research are worth mentioning (for instance, publication of a large, randomized clinical trial with surprising results), they should be described as being from a single study, for example:

"A large, NIH-funded study published in 2010 found that selenium and Vitamin E supplements increased the risk of prostate cancer; it was thought they would prevent prostate cancer." (citing PMID 20924966)

After enough time has passed for a review in the area to be published, the review should be cited in preference to the primary study. Using a secondary source often allows the fact to be stated with greater reliability:

"Supplemental Vitamin E and selenium increase the risk of prostate cancer." (citing PMID 23552052)

If no review on the subject is published in a reasonable amount of time, then the content and primary source should be removed.

A reason to avoid primary sources in the biomedical field—especially papers reporting results of in vitro experiments—is that they are often not replicable[2][3][4] and are therefore unsuitable for use in generating encyclopedic, reliable content about health. Drug discovery scientists at Bayer in 2011 reported that they were able to replicate results in only ~20–25% of the prominent studies they examined;[5] scientists from Amgen followed with a publication in 2012 showing that they were only able to replicate 6 (11%) of 53 high-impact publications and called for higher standards in scientific publishing.[6] The journal Nature announced in April 2013 that in response to these and other articles showing a widespread problem with reproducibility, it was taking measures to raise its standards.[7] Further, the fact that a claim is published in a refereed journal need not make it true. Even a well-designed randomized experiment can (with low probability) produce spurious results. Experiments and studies can produce flawed results or fall victim to deliberate fraud (See: the Retracted article on dopaminergic neurotoxicity of MDMA and the Schön scandal.)

Summarize scientific consensus

Scientific journals are the best place to find both primary source articles about experiments, including medical studies, and secondary sources. Every rigorous scientific journal is peer reviewed. Be careful of material published in a journal that lacks peer review or that reports material in a different field. (See: Martin Rimm.) Be careful of material published in disreputable journals or disreputable fields. (See: Sokal affair.)

PhysicsWiki policies on the neutral point of view and not publishing original research demand that we present any prevailing medical or scientific consensus, which can be found in recent, authoritative review articles, in statements and practice guidelines issued by major professional medical or scientific societies (for example, the European Society of Cardiology or the Infectious Disease Society of America) and widely respected governmental and quasi-governmental health authorities (for example, AHRQ, USPSTF, NICE, and WHO), in textbooks, or in some forms of monographs. Although significant-minority views are welcome in PhysicsWiki, such views must be presented in the context of their acceptance by experts in the field. Additionally, the views of tiny minorities need not be reported.

Finally, make readers aware of controversies that are stated in reliable sources. A well-referenced article will point to specific journal articles or specific theories proposed by specific researchers.

Assess evidence quality

Knowing the quality of the evidence helps editors distinguish between minority and majority viewpoints, determine due weight, and identify information that will be accepted as evidence-based medicine. Not all papers in even reputable medical journals can be treated as equivalent. Studies can be categorized into a number of levels,[8] and in general, editors should rely upon high-quality evidence, such as systematic reviews, rather than lower-quality evidence, such as case reports, or non-evidence, such as anecdotes or conventional wisdom. The medical guidelines or position statements produced by nationally or internationally recognised expert bodies often contain an assessment of the evidence as part of the report.

The best evidence comes primarily from meta-analyses of randomized controlled trials (RCTs).[9] Systematic reviews of bodies of literature of overall good quality and consistency addressing the specific recommendation have less reliability when they include non-randomized studies.[10] Narrative reviews can help establish the context of evidence quality. Roughly in descending order of quality, lower-quality evidence in medical research comes from individual RCTs; other controlled studies; quasi-experimental studies; non-experimental, prospective, observational studies, such as cohort studies and case control studies; cross-sectional studies (surveys), and other correlation studies such as ecological studies; retrospective analyses; and non-evidence-based expert opinion or clinical experience. Case reports, whether in the popular press or a peer reviewed medical journal, are a form of anecdote and generally fall below the minimum requirements of reliable medical sources.

Speculative proposals and early-stage research should not be cited in ways that suggest wide acceptance. For example, the results of an early-stage clinical trial are unlikely to be appropriate for inclusion in the Treatment section of an article about a disease because a possible future treatment has little bearing on current treatment practice. However, the results might—in some cases—be appropriate for inclusion in an article dedicated to the treatment in question or to the researchers or businesses involved in it. Such information, particularly if citing a secondary source, might also be appropriate for a well-documented section on research directions in an article about a disease. To prevent misunderstandings, the text should clearly identify the level of research cited (e.g., "first-in-human safety testing").

Several formal systems exist for assessing the quality of available evidence on medical subjects.[11][12] "Assessing evidence quality" means that editors should determine the quality of the type of study. Editors should not perform a detailed academic peer review. Do not reject a high-quality type of study due to personal objections to the study's inclusion criteria, references, funding sources, or conclusions.

Avoid over-emphasizing single studies, particularly in vitro or animal studies

In vitro studies and animal models serve a central role in biomedical research, and are invaluable in determining mechanistic pathways and generating hypotheses. However, in vitro and animal-model findings do not translate consistently into clinical effects in human beings. Where in vitro and animal-model data are cited on PhysicsWiki, it should be clear to the reader that the data are pre-clinical, and the article text should avoid stating or implying that the reported findings hold true in humans. The level of support for a hypothesis should be evident to the reader.

Use of small-scale, single studies make for weak evidence, and allow for easy cherry picking of data. Results of studies cited or mentioned in PhysicsWiki should be put in context by using high quality secondary sources rather than using the primary sources themselves.

Use up-to-date evidence

Here are some rules of thumb for keeping an article up-to-date, while maintaining the more-important goal of reliability. These instructions are appropriate for actively researched areas with many primary sources and several reviews and may need to be relaxed in areas where little progress is being made or few reviews are being published.

  • Look for reviews published in the last five years or so, with newer being better. The range of reviews you examine should be wide enough to catch at least one full review cycle, containing newer reviews written and published in the light of older ones and of more-recent primary studies.
  • Within this range, assessing them may be difficult. While the most-recent reviews include later research results, do not automatically give more weight to the review that happens to have been published most recently, as this is recentism.
  • Prefer recent reviews to older primary sources on the same topic. If recent reviews do not mention an older primary source, the older source is dubious. Conversely, an older primary source that is seminal, replicated, and often-cited in reviews can be mentioned in the main text in a context established by reviews. For example, the article genetics might mention Darwin's 1859 book On the Origin of Species as part of a discussion supported by recent reviews.

These rules of thumb have several exceptions:

  • History sections often cite older work for obvious reasons.
  • Cochrane Library reviews are generally of high-quality and are routinely maintained even if their initial publication dates fall outside the above window.
  • A newer source which is of lower quality does not necessarily supersede an older source of higher quality.

Use independent sources

Many medical claims lack reliable research about the efficacy and safety of proposed treatments or about the legitimacy of statements made by proponents. In such cases, reliable sources may be difficult to find while unreliable sources are readily available. Whenever writing about medical claims not supported by mainstream research, it is vital that third-party, independent sources be used. Sources written and reviewed by the advocates of such marginal ideas can be used to describe personal opinions, but extreme care should be taken when using such sources lest the more controversial aspects of their opinions be taken at face value or, worse, asserted as fact. If the independent sources discussing a medical subject are of low quality, then it is likely that the subject itself is not notable enough to have its own article or relevant enough to be mentioned in other articles.

Choosing sources

Montage with central stripe reading "PLoS MEDICINE". Other images are orange segments, a woman in a blue shawl carrying a food package labeled "USA", a pregnant woman holding hands with a child, a hand holding several different pills over a lap covered by a colorful dress, patients in a hospital, and pills on a leaf.
PLoS Medicine and other open access journals can be useful as sources for images in PhysicsWiki articles. Because the above image was published under the terms of a Creative Commons license, it can be uploaded to Wikimedia Commons and used on PhysicsWiki. Click on the above image to find its source.

A PhysicsWiki article should cite high-quality reliable sources regardless of whether they require a fee or a subscription. When all else is equal, it is better to cite a source with a full text that is freely readable so that readers can follow the link to the source. Some high-quality journals, such as JAMA, publish a few freely readable articles even though most are not free. A few high-quality journals, such as PLoS Medicine, publish only freely readable sources. Also, a few sources are in the public domain; these include many U.S. government publications, such as the Morbidity and Mortality Weekly Report of the Centers for Disease Control and Prevention.

When searching for biomedical sources, it is wise to skim-read everything available, including abstracts of papers that are not freely readable, and use that to get a feel for what reliable sources are saying. However, when it comes to actually writing a PhysicsWiki article, it is misleading to give a full citation for a source after reading only its abstract; the abstract necessarily presents a stripped-down version of the conclusions and omits the background that can be crucial for understanding exactly what the source says. To access the full text, the editor may need to visit a medical library or ask someone at the WikiProject Resource Exchange or WikiProject Medicine's talk page to either provide an electronic copy or read the source and summarize what it says; if neither is possible, the editor may need to settle for using a lower-impact source.

Biomedical journals

Peer-reviewed medical journals are a natural choice as a source for up-to-date medical information in PhysicsWiki articles. They contain a mixture of primary and secondary sources. Journal articles come in many types, including original research ranging from vast studies to individual case reports, reviews, editorials and op-ed pieces, advocacy pieces, speculation, book reviews, letters to the editor and other forms of commentary or correspondence, biographies, and eulogies. It is usually best to use reviews and meta-analyses where possible. Reviews in particular give a balanced and general perspective of a topic, and are usually easier to understand.

As mentioned above, the biomedical literature contains two major types of sources: primary publications describe novel research for the first time, while review articles summarize and integrate a topic of research into an overall view. In medicine, primary sources include clinical trials, which test new treatments. Broadly speaking, reviews may be narrative or systematic (and sometimes both). Narrative reviews often set out to provide a general summary of a topic based on a survey of the literature. Systematic reviews tend to use sophisticated methodology to address a particular clinical question in as balanced (unbiased) a way as possible. Some systematic reviews also include a statistical meta-analysis to combine the results of several clinical trials to provide stronger quantitative evidence about how well a treatment works for a particular purpose. Systematic reviews and meta-analyses of randomized comparative (or controlled) trials can provide strong evidence of the clinical efficacy of particular treatments in given scenarios, which may in turn be incorporated into medical guidelines or institutional position papers (ideal sources for clinical evidence). More general narrative reviews can be useful sources when outlining a topic.

Research papers that describe original experiments are primary sources. However, they normally contain introductory, background, or review sections that place their research in the context of previous work; these sections may be cited in PhysicsWiki with care. These sections are often incomplete[13] and typically less useful or reliable than reviews or other sources, such as textbooks, which are intended to be reasonably comprehensive. If challenged by another editor in good faith, the primary source should be supplemented with a more appropriate source. A general narrative review of a subject by an expert in the field can make a good secondary source covering various aspects of a subject within a PhysicsWiki article. Such reviews typically do not contain primary research, but can make interpretations and draw conclusions from primary sources that no PhysicsWiki editor would be allowed to do. A systematic review uses a reproducible methodology to select primary (or sometimes secondary) studies meeting explicit criteria to address a specific question. Such reviews should be more reliable and accurate and less prone to bias than a narrative review.[11] However, whereas a narrative review may give a panorama of current knowledge on a particular topic, a systematic review tends to have a narrower focus.

Some journals specialize in particular article types. A few, such as Evidence-based Dentistry (ISSN 1462-0049), publish third-party summaries of reviews and guidelines published elsewhere. If an editor has access to both the original source and the summary, and finds both helpful, it is good practice to cite both sources together (see: Formatting citations for details). Others, such as Journal of Medical Biography, publish historical material that can be valuable for History sections, but is rarely useful for current medicine. Still others, such as Medical Hypotheses, publish speculative proposals that are not reliable sources for biomedical topics.

The Abridged Index Medicus provides a list of 114 selected "core clinical journals" (this subset of the medical literature can be searched in PubMed using a 'journal categories' filter).[14][15] Another useful grouping of core medical journals is the 2003 Brandon/Hill list, which includes 141 publications selected for a small medical library[16] (although this list is no longer maintained, the listed journals are of high quality). Core general medical journals include the New England Journal of Medicine, The Lancet, the Journal of the American Medical Association (JAMA), the Annals of Internal Medicine, the British Medical Journal (BMJ), and the Canadian Medical Association Journal. Core basic science and biology journals include Nature, Science and Cell.

An integral part of finding high quality sources is avoiding articles from journals without a reputation for fact-checking and accuracy. A red flag that a journal article is probably not reliable for health claims might be publication by a publisher that has a reputation for exhibiting "predatory" behavior, which includes questionable business practices and/or peer-review processes that raise concerns about the reliability of their journal articles. (See "References" section below for examples of such publishers.[17][18]) Other indications that a biomedical journal article may not be reliable are its publication in a journal that is not indexed in the bibliographic database MEDLINE,[19] or its content being outside the journal's normal scope (for instance, an article on the efficacy of a new cancer treatment in a psychiatric journal or the surgical techniques for hip replacement in a urology journal). Determining the reliability of any individual journal article may also take into account whether the article has garnered significant positive citations in sources of undisputed reliability, suggesting wider acceptance in the medical literature despite any red flags suggested here.


Medical textbooks published by academic publishers are often excellent secondary sources. If a textbook is intended for students, it may not be as thorough as a monograph or chapter in a textbook intended for professionals or postgraduates. Ensure that the book is up to date, unless a historical perspective is required. Doody's maintains a list of core health sciences books, which is available only to subscribers.[20] Major academic publishers (e.g., Elsevier, Springer Verlag, Wolters Kluwer, and Informa) publish specialized medical book series with good editorial oversight; volumes in these series summarize the latest research in narrow areas, usually in a more extensive format than journal reviews. Specialized biomedical encyclopaedias published by these established publishers are often of good quality, but as a tertiary source, the information may be too terse for detailed articles.

Additionally, popular science and medicine books are useful sources, which may be primary, secondary, or tertiary, but there are exceptions. Most self-published books or books published by vanity presses undergo no independent fact-checking or peer review and, consequently, are not reliable sources. Books published by university presses or the National Academy of Sciences, on the other hand, tend to be well-researched and useful for most purposes.

Medical and scientific organizations

Statements and information from reputable major medical and scientific bodies may be valuable encyclopedic sources. These bodies include the U.S. National Academies (including the Institute of Medicine and the National Academy of Sciences), the British National Health Service, the U.S. National Institutes of Health and Centers for Disease Control and Prevention, and the World Health Organization. The reliability of these sources range from formal scientific reports, which can be the equal of the best reviews published in medical journals, through public guides and service announcements, which have the advantage of being freely readable, but are generally less authoritative than the underlying medical literature.

Popular press

The popular press is generally not a reliable source for scientific and medical information in articles. Most medical news articles fail to discuss important issues such as evidence quality,[21] costs, and risks versus benefits,[22] and news articles too often convey wrong or misleading information about health care.[23] Articles in newspapers and popular magazines generally lack the context to judge experimental results. They tend to overemphasize the certainty of any result, for instance, presenting a new and experimental treatment as "the cure" for a disease or an every-day substance as "the cause" of a disease. Newspapers and magazines may also publish articles about scientific results before those results have been published in a peer reviewed journal or reproduced by other experimenters. Such articles may be based uncritically on a press release, which can be a biased source even when issued by an academic medical center.[24] News articles also tend neither to report adequately on the scientific methodology and the experimental error, nor to express risk in meaningful terms. For PhysicsWiki's purposes, articles in the popular press are generally considered independent, primary sources.

A news article should therefore not be used as a sole source for a medical fact or figure. Editors are encouraged to seek out the scholarly research behind the news story. One possibility is to cite a higher-quality source along with a more-accessible popular source, for example, with the |laysummary= parameter of {{cite journal}}.

Conversely, the high-quality popular press can be a good source for social, biographical, current-affairs, financial, and historical information in a medical article. For example, popular science magazines such as New Scientist and Scientific American are not peer reviewed, but sometimes feature articles that explain medical subjects in plain English. As the quality of press coverage of medicine ranges from excellent to irresponsible, use common sense, and see how well the source fits the verifiability policy and general reliable sources guidelines. Sources for evaluating health-care media coverage include the review websites Behind the Headlines, Health News Review,[1] and Media Doctor, along with specialized academic journals, such as the Journal of Health Communication; reviews can also appear in the American Journal of Public Health, the Columbia Journalism Review, the Bad Science column in The Guardian, and others. Health News Review's criteria for rating news stories[25] can help to get a general idea of the quality of a medical news article.

Other sources

Reliable sources must be strong enough to support the claim. A lightweight source may sometimes be acceptable for a lightweight claim, but never for an extraordinary claim.

Press releases, newsletters, advocacy and self-help publications, blogs and other websites, and other sources contain a wide range of biomedical information ranging from factual to fraudulent, with a high percentage being of low quality. Conference abstracts present incomplete and unpublished data and undergo varying levels of review; they are often unreviewed and their initial conclusions may have changed dramatically if and when the data are finally ready for publication.[26] Consequently, they are usually poor sources and should always be used with caution, never used to support surprising claims, and carefully identified in the text as preliminary work. Peer-reviewed medical information resources such as WebMD, UpToDate, and eMedicine are usually acceptable sources for uncontroversial information; however, as much as possible PhysicsWiki articles should cite the more established literature directly.

Searching for sources

Search engines are commonly used to find biomedical sources. Each engine has quirks, advantages, and disadvantages, and may not return the results that the editor needs unless used carefully. It typically takes experience and practice to recognize when a search has not been effective; even if an editor finds useful sources, they may have missed other sources that would have been more useful or they may generate pages and pages of less-than-useful material. A good strategy for avoiding sole reliance on search engines is to find a few recent high-quality sources and follow their citations to see what the search engine missed. It can also be helpful to perform a plain web search rather than one of scholarly articles only.

PubMed is an excellent starting point for locating peer reviewed medical literature reviews on humans from the last five years . It offers a free search engine for accessing the MEDLINE database of biomedical research articles offered by the National Library of Medicine at the U.S. National Institutes of Health.[27] There are basic and advanced options for searching PubMed.[15] For example, clicking on the "Review" tab will help narrow the search to review articles. The "Limits" tab can further limit the search, for example, to meta-analyses, to freely readable sources, and/or "core clinical journals". Although PubMed is a comprehensive database, many of its indexed journals restrict online access. Another website, PubMed Central, provides free access to full texts. While it is often not the official published version, it is a peer reviewed manuscript that is substantially the same, but lacks minor copy-editing by the publisher.[28]

When looking at an individual abstract on the PubMed website, an editor can click on "Publication Types, MeSH Terms" at the bottom of the page to see how PubMed has classified a document. For example, a page that is tagged as "Comment" or "Letter" is a non-peer reviewed letter to the editor. The classification scheme includes about 70 types of documents.[2] For medical information, the most useful types of articles are typically labeled "Guideline", "Meta-analysis", "Practice guideline", or "Review".

See also


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  4. Nature's Challenges in Reproducibility initiative
  5. Prinz F et al. Believe it or not: how much can we rely on published data on potential drug targets? Nature Reviews Drug Discovery 10, 712 (September 2011) | doi:10.1038/nrd3439-c1
  6. C. Glenn Begley & Lee M. Ellis Drug development: Raise standards for preclinical cancer research Nature 483, 531–533 (29 March 2012) doi:10.1038/483531a
  7. Editors of Nature. April 24 2013 Announcement: Reducing our irreproducibility
  8. PMID 17473152 (PMID 17473152)
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  19. To determine if a journal is MEDLINE indexed, go to this website, and search for the name of the journal. On the journal page, under the heading "Current Indexing Status", you can see whether or not the journal is currently indexed. Note that journals that have changed names or ceased publication will not be "currently" indexed on MEDLINE, but their indexing status, when they were being published, can be viewed under other headings on that same page.
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  26. PMID 15857882 (PMID 15857882)
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Further reading

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  • Lua error in Module:Citation/CS1 at line 746: Argument map not defined for this variable. This is derived from a prepublication version of a series published in JAMA.