Wikipedia:Identifying primary and secondary sources for biology articles

Throughout Wikipedia there are essays, guidelines and policy articles about the suitability of sources for editing article content, for example, the reliability of sources and the verifiability of content. These have been written because a cornerstone policy of Wikipedia is not to use original research. One of the ways of avoiding original research in articles is to use only primary, secondary or tertiary sources. Wikipedia articles should be based on reliable, published secondary sources and, to a lesser extent, on tertiary sources and primary sources. Secondary or tertiary sources are needed to establish the topic's notability and to avoid novel interpretations of primary sources. All interpretive claims, analyses, or synthetic claims about primary sources must be referenced to a secondary source, rather than to an original analysis of the primary-source material by Wikipedia editors.

Despite the fundamental importance of using primary and secondary sources, the difference between these is sometimes unclear; the information required to assess whether a source, or part of a source, is primary or secondary is often contained in rather long, detailed, general guidelines which might also be covering Art, History, Law, etc. The aim of this essay is to provide immediately accessible, concise information for users editing Biology articles, specifically about whether sources, or their sections, should be considered as primary or secondary.

Definitions

 * Primary sources are original materials that are close to an event, and are often accounts written by people who are directly involved. They offer an insider's view of an event, a period of history, a work of art, a political decision, and so on. Primary sources may or may not be independent or third-party sources. A scientific paper documenting a new experiment conducted by the author is a primary source on the outcome of that experiment.


 * Secondary sources provide an author's own thinking based on primary sources, generally at least one step removed from an event. It contains an author's interpretation, analysis, or evaluation of the facts, evidence, concepts, and ideas taken from primary sources. Secondary sources are not necessarily independent or third-party sources. They rely on primary sources for their material, making analytic or evaluative claims about them.


 * Tertiary sources are publications such as encyclopedias and other compendia that summarize primary and secondary sources. Wikipedia is a bad source. While it is a tertiary source, Wikipedia is not considered a reliable source for Wikipedia articles.  Tertiary sources can provide a valuable overview of a topic, but often oversimplify complex material. It is usually better to cite the secondary or primary literature directly.

Scientific journals
Good quality scientific journals publish articles that have been subject to peer review. This is the evaluation of work by one or more people of similar competence to the producers of the work (peers). It constitutes a form of self-regulation by qualified members of a profession within the relevant field. Peer review of an article does not mean the article is a review.

Original papers
A widely used source of content for Biology articles are original papers published in science journals. Despite their being so widely used as sources, there is sometimes confusion about the primary or secondary nature of original papers. Many scientific journal papers are based on sections, frequently, the Abstract, Introduction, Methods, Results and Discussion. The confusion arises because some of these sections are a primary source, other sections are a secondary source, and some are both. For example, the following sentence might appear in the Abstract, Discussion, or possibly Introduction, and contains both primary and secondary source material.

The Abstract summarises the entire paper and therefore discusses both the new findings and previous research related to the subject matter. The Abstract often contains bold statements that are attractive to include in a Biology article, however, abstracts can be unreferenced and therefore it can be difficult to decide whether it is a primary or secondary source.

The Introduction is essentially a review of the published research related to the subject matter of the paper. The Introduction will often contain sentences that indicate the authors have expertly reviewed the published material. For example, the paper may state "There is ample evidence that X is a risk-factor for Y (Reference1, Reference2, Reference3)." This type of statement means because experts (the authors of the original paper) have reviewed the information, the source is secondary for that content. However, the Introduction may also state "In this study, we further build on our previous finding that X leads to Y (Reference1)". In this case, the relationship of "X leads to Y" has apparently not been subjected to external review and is therefore a primary source.

The Methods describes what was done in the study. It is usually a primary source, but in some circumstances may be a secondary source, e.g. it may contain a sentence which states "We used the calibration method proposed by Reference1 which was subsequently verified by Reference2, Reference3 and Reference4". (Note: The references must be to authors other than the authors of the original paper.)

The Results presents the data or facts generated by the study. It is a primary source; it usually presents novel material that has not been subject to widespread scrutiny (although it will have been seen by one or more expert reviewers before publication). The Discussion interprets the new findings and integrates these into the context of already published research. So, if there is a statement that "The present study shows substance X had an analgesic effect on cats", the article is a primary source for this content. However, if the statement is "The present study shows that substance X had an analgesic effect on cats, thereby supporting the review of Reference1" the statement can be considered a secondary source for this content. (Note: It might be considered a higher standard of editing to research and cite the original review article Reference1.)

Because the different sections of an original paper can be considered as primary, secondary, or both, care is needed when editing using an original paper as the source material. Similarly, an edit using an original paper should not be immediately classified as primary and omitted/deleted on this basis alone. It is the source of the content edited in Wikipedia that is important, not necessarily the source as a whole.

Narrative reviews
Some science journals publish narrative reviews. A general narrative review of a subject by an expert in the field makes a good secondary source that can be used to cover various aspects of a subject within a Wikipedia article. Such reviews typically contain no original data, but can make interpretations and draw conclusions from primary sources that no Wikipedia editor would be allowed to do.

Systematic reviews
Science journals may also publish systematic reviews. These use a reproducible method to select primary studies meeting explicit criteria to answer a specific question. Such reviews should be more reliable, accurate and less prone to bias than a narrative review. However, a systematic review's focus on answering one question limits its use as a source on Wikipedia.

Meta-analysis
Meta-analysis is a statistical method for combining results from different studies to identify patterns among study results, sources of disagreement among those results, or other interesting relationships that may come to light in the context of multiple studies. Meta-analysis can be thought of as "conducting research about previous research." Meta-analysis studies are considered secondary sources because they are based on and analyze or interpret (rather than merely citing or describing) original experimental reports.

Books
Many introductory undergraduate-level textbooks are regarded as tertiary sources because they sum up multiple secondary sources.

Popular science books can also be useful tertiary sources, though information may be oversimplified or lacking in nuance or the full range of opinion in a field may not be adequately represented. For example, The Selfish Gene describes Richard Dawkins' synthesis of previously published work to formulate a novel hypothesis. Because it was the first account of the selfish gene principle, it is a primary source for the principle; if you are discussing the selfish gene principle, it is better to find a secondary source, e.g. a review of the book.

Most books and monographs that are self-published or published by vanity presses undergo no independent fact-checking or peer review and consequently are primary and unreliable sources.

Popular press
High-quality popular press can be a good source for social, biographical, current-affairs, financial, and historical information in a biology article. For example, popular science magazines such as New Scientist and Scientific American are not peer reviewed (and therefore may be primary sources), but sometimes feature articles that explain biology subjects in plain English.

Newspapers can be both primary and secondary sources. For example, if a newspaper reported an eye-witness account that a tiger had killed a person in a village, this would be a primary source. It would not be suitable to use this source to indicate that all tigers are "man-killers", however, it might be appropriate to include this source on a list of reported fatalities due to attacks by tigers. Newspaper articles are sometimes secondary sources. For example, there may be an article where the reporter uses government data to report on the annual number of badgers being culled in the UK. Editors should be aware that newspaper reporters are not always experts in the subject and may not be scientifically accurate with their language. For example, the word "significant" to a scientist has a precise statistical meaning. To a reporter, it generally means a finding is "noteworthy" - whether the finding reached statistical significance may have little relevance to the reporter.

Guidelines for medical articles take a much dimmer view of using newspaper articles. WP:MEDRS states that the popular press is generally not a reliable source for scientific and medical information, and furthermore newspapers should not be used as a sole source for a medical fact or figure. However, WP:MEDRS also indicates that the high-quality popular press can be a good source for social, biographical, current-affairs, financial and historical information in a medical article.

Other sources
Press releases, blogs, newsletters, advocacy and self-help publications are generally considered to be primary sources, with a high percentage being of low quality. However, some may contain information that is acceptable such as the "mission statement" of an advocacy group.