How to Find and Use Grey Literature in a Literature Review (2026)

Grey literature is research produced outside commercial journal publishing: government and NGO reports, theses and dissertations, working papers, conference papers, preprints, and policy documents. You include it in a literature review to catch evidence that never reached a journal, which reduces publication bias, and you appraise each grey source harder than a peer-reviewed one because it has not been through peer review. The practical route is to search institutional repositories, Google Scholar, government and organisation websites, and dissertation databases, then screen each source with a checklist like AACODS before you cite it.

It is the richest seam most postgraduate students walk straight past. This guide covers what counts as grey literature, why it belongs in a serious review, exactly where to look, how to judge whether a grey source is trustworthy, and how to cite it once you have decided to keep it.

What Is Grey Literature, and What Counts as It?

Grey literature is any research or information produced by government, academia, business, or industry that is not controlled by commercial publishers and has usually not been peer reviewed. Journal articles and academic books are white literature because a publisher and peer review stand behind them. Grey literature covers everything credible that sits outside that system, from a national health department report to a doctoral thesis to a preprint posted the week before you searched.

The category is broad, so here are the main types with what each one is actually good for.

The common thread is that no journal gatekeeper has vetted these sources, so they reach you faster and cover more ground, and they carry more of the appraisal burden onto you.

Why Should I Include Grey Literature in a Literature Review?

Include grey literature because relying only on published journal articles bakes publication bias into your review. Journals disproportionately publish studies with positive, statistically significant results, so a study that found no effect often ends up unpublished, a pattern long known as the file drawer problem. A review built only from journals can therefore overstate how strong or settled an effect is, because the null results are sitting in theses, reports, and unpublished trials you never searched.

Grey literature also buys you recency and reach. A government report can carry this year’s figures while the journal version is two years away, a thesis can hold the detailed method a four page article had to cut, and an NGO evaluation can describe how an intervention actually behaved in the field. As of August 2026 most systematic review guidance treats a grey literature search as expected rather than optional, precisely because leaving it out is now recognised as a source of bias rather than a matter of taste.

Where Do I Find Grey Literature?

Find grey literature by searching repositories, subject-specific databases, and the websites of the organisations that produce it, because most grey sources are never indexed the way journal articles are. There is no single grey literature database that covers everything, so you combine a few targeted searches rather than running one search box.

Keep a simple log of where you searched, the terms you used, and the date, the same way you would for a database search. When a marker asks how thorough your review was, being able to say you searched three repositories and four organisation sites on a given date is the difference between a defensible search and a vague one.

How Do I Judge Whether a Grey Source Is Trustworthy? The AACODS Checklist

Judge a grey source with the AACODS checklist, a six-point appraisal tool built specifically for grey literature because the usual was-it-peer-reviewed shortcut does not apply. AACODS stands for Authority, Accuracy, Coverage, Objectivity, Date, and Significance, and you run a source through all six before you rely on it.

1. Authority. Who produced it, and do they have standing to? A national statistics office and an anonymous blog post are not the same kind of claim.

2. Accuracy. Are the method and the data stated clearly enough to trust the findings? If you cannot tell how many people were studied, you cannot cite the number.

3. Coverage. What does the source include and exclude? Knowing its limits is what stops you stretching one region’s result into a general one.

4. Objectivity. Does the producer have a stake in the conclusion? This is the one that matters most for industry and advocacy reports, and it is the most common reason to drop a source.

5. Date. Is it current enough for your question? Grey literature is often used for exactly this, so an undated document is a real problem.

6. Significance. Does it add something your peer-reviewed sources do not? If it only repeats them, it is padding.

A source that passes all six earns a place in your review, and one that fails Objectivity or Accuracy usually does not, however convenient its numbers are.

How Do I Cite Grey Literature?

Cite grey literature with the same core parts you use for any source, adapted to the document type: author or producing organisation, year, title, the kind of document, and where you found it, including a URL and access date for anything online. Referencing styles handle this explicitly. APA and Harvard both have formats for reports, theses, and web documents, so a government report is cited as a report by its issuing body, and a thesis is cited by its author with the degree and awarding institution named.

The one rule that trips people up is the organisation as author. When no person is named, the producing body is the author, so a health department report is cited under the department’s name, not left authorless. For anything you accessed online, record the URL and the date you retrieved it, because grey literature moves and disappears far more often than journal articles do, and an access date shows exactly which version you read.

Can I Use Grey Literature With an AI Literature Review Tool?

Yes, an AI literature review tool can work with grey literature as long as it works from documents you upload rather than a fixed journal index, because grey sources are exactly the ones a closed database will not contain. Litrevu is an AI literature review assistant that turns the papers a researcher has already gathered into a cited first draft, with every citation traceable to the uploaded source. That upload-based design means a government report PDF, a thesis, and a journal article sit side by side in the same draft, each claim linked back to the specific file it came from.

To illustrate the format, here is the shape a synthesis paragraph takes when it mixes grey and peer-reviewed sources on one theme:

Theme: effectiveness of community health worker programmes. A national programme evaluation reports a fall in missed appointments after rollout [Source: DoH_CHW_Evaluation2024.pdf, p.19], which two peer-reviewed trials support in smaller samples [Source: Naicker2023.pdf, p.6] [Source: Osei2022.pdf, p.14], though the evaluation and the trials measure effectiveness differently, leaving the comparison looser than it first appears.

The point of the example is the shape, not the content. A draft treats the government evaluation and the journal trials as equal citations while flagging that they do not measure the same thing, which is exactly the judgement grey literature demands. A draft like this is a starting point you appraise and rewrite, never a finished review, and each source stays pinned to a file and a page so you can open it and run your own AACODS check before you trust it.

Frequently Asked Questions

What is grey literature in simple terms?

Grey literature is research that is not published in journals or academic books, such as government reports, theses, preprints, and organisation reports. It is called grey because it sits between formally published work and unpublished private documents. It is usually free to read but has not been peer reviewed, so you judge its quality yourself.

Is grey literature a reliable source?

Grey literature can be reliable, but reliability varies far more than with peer-reviewed articles, so you appraise each source individually. A national statistics report from a government agency is often highly reliable, while an industry white paper with a commercial interest needs more caution. Running each source through the AACODS checklist, which covers authority, accuracy, coverage, objectivity, date, and significance, is the standard way to decide.

Should I include grey literature in a literature review?

In most cases yes, because leaving it out risks publication bias, the tendency for journals to publish positive results and leave null findings unpublished. Including grey literature captures those missing null results, recent data, and practitioner evidence. The exception is a review with a narrow scope that explicitly limits itself to peer-reviewed work, in which case you say so and explain why.

Where can I find grey literature for free?

Most grey literature is free through institutional repositories, government and NGO websites, Google Scholar, preprint servers, and national thesis portals. Unlike journal articles behind paywalls, grey literature is usually posted openly by the body that produced it. Searching an organisation’s own website directly often finds reports that a general search engine buries.

How do I cite a government report or thesis?

Cite a government report under the issuing body as author, with the year, title, document type, and URL with access date if it is online. Cite a thesis under its author’s name, with the year, title, the degree, and the awarding institution. Both APA and Harvard have specific formats for reports and theses, so check which one your department requires.