Boolean search for research papers comes down to three words and three symbols. AND, OR and NOT decide which records match; quotation marks hold a phrase together, an asterisk stands for any ending, and brackets set the reading order. On 2 October 2026 the words test anxiety, typed loose, matched 1,976,440 published works. As one exact phrase, they matched 42,482.
No two search engines read those symbols in quite the same way. EdCitation publishes this guide, built from the help pages of PubMed, Scopus, OpenAlex and Google Scholar, three university library guides, the Cochrane Handbook and the reporting guidelines for review searches, all read on 2 October 2026.
That phrase test is one EdCitation runs free, with no account: the Match my words option in Find sources searches your words as one exact phrase, in titles only, or both, and the search box accepts AND, OR and NOT. Everything it returns is a published record that was looked up. EdCitation never writes any part of anyone's work.
What do AND, OR and NOT do in a search?
AND keeps records that contain every term, OR keeps records that contain any of them, and NOT throws out records that contain a term. For a review, the Cochrane Handbook sets the pattern: synonyms for one concept are joined with OR, and the concepts are joined with AND (Lefebvre et al., 2025). The examples below show each operator and its trap.
| Operator | Keeps | Example | Trap |
|---|---|---|---|
| AND | Every term | "test anxiety" AND students | Each extra AND loses papers worded differently |
| OR | Any term | exam OR test OR examination | Unbracketed, it swallows the rest of the string |
| NOT | Records without the term | "moral injury" NOT veterans | Removes papers that merely mention the word |
| None | Usually read as AND | test anxiety | Some engines also rank by closeness |
| Match my words in Find sources | One phrase, titles only, or both | test anxiety, As one exact phrase | Narrows hard: 4,746 of 1,976,440 in our run |
NOT, used sparingly
The Cochrane Handbook says to avoid NOT where possible, because it can quietly remove relevant records (Lefebvre et al., 2025). The University of Edinburgh (n.d.) also urges caution, and notes NOT is little used in the arts and humanities. The run further down shows what one NOT did to a search of nursing papers.
Capitals and the invisible AND
PubMed and OpenAlex both ask for operators in capitals, and OpenAlex joins words that have no operator between them with AND (OpenAlex, 2026). The Penn Libraries catalogue adds a trick: inside quotation marks, operators stop working, so a quoted "Pride and Prejudice" is searched as one phrase (Penn Libraries, 2025).
How does exact phrase search work?
Quotation marks around two or more words ask for those words together, in that order. The Edinburgh guide's caveat matters: some databases do not support phrase searching, and some use another symbol, so read the help page first.
Scopus: a loose phrase and an exact one
In Scopus, straight double quotation marks give a loose phrase that accepts plurals and spelling variants: a quoted heart attack also finds heart attacks, and anesthesia finds anaesthesia. Braces give the strict version, so {oyster toadfish} matches only that phrase (Elsevier, 2026).
PubMed: the phrase index
In PubMed, quotation marks switch off automatic term mapping and send the phrase to a phrase index. The National Library of Medicine (n.d.) warns that a phrase can appear in a record without being in that index. Its fix is a proximity search of zero: "cognitive impairment"[tiab:~0] finds the two words side by side, in either order, in the title or abstract. Proximity works only in the Title, Title/Abstract and Affiliation fields.
OpenAlex: stemming and closeness
OpenAlex reduces unquoted words to their stems, so possums also finds possum, and drops words such as "the". Quotation marks ask for the exact phrase, and "test anxiety"~3 lets the words sit up to three positions apart. For works, OpenAlex searches the title, the abstract and the full text (OpenAlex, 2026).
Straight quotes, not curly ones
Scopus warns that curly quotation marks can stop it reading a query, and says to check the quotes in any string copied from Word, Google Docs, a reference manager, a PDF or a web page (Elsevier, 2026). Keep search strings in a plain text file.
How do truncation, wildcards and brackets work?
Truncation puts an asterisk after a stem to find every ending. The Edinburgh guide's teen* finds teen, teens, teenager and teenagers; Utah State University Libraries (2026) give music* for musical, musician and musicality. The asterisk is common, not universal.
Each engine sets a minimum stem: four letters in PubMed, where truncating also turns off automatic term mapping (National Library of Medicine, n.d.), and three in OpenAlex. Short stems pull in strangers: test* finds testosterone and testimony. Some stems help: program* catches both program and programme.
A wildcard, usually a question mark, stands for one character inside a word: organi?ation, wom?n and col?r each cover two spellings. Penn's catalogue will not truncate inside a quoted phrase, though some databases will.
Brackets, because the reading order differs
The engines disagree on which operator comes first. Utah State's guide says databases usually process AND first; Scopus processes OR first, then proximity, then AND, then AND NOT (Elsevier, 2026); PubMed reads left to right. Take anxiety AND exam OR test:
- PubMed reads (anxiety AND exam) OR test, returning every record containing test.
- Scopus reads anxiety AND (exam OR test), probably what was meant.
Written as anxiety AND (exam OR test), the string means the same everywhere. Bracket every OR group.
How do I run a Boolean search for research papers in different databases?
Write one master string, then adapt it to each engine. The rows below come from each service's own help pages, read on 2 October 2026.
| Engine | Operators | Phrases | Truncation | Worth knowing |
|---|---|---|---|---|
| PubMed | Capitals, read left to right | Quotes; [tiab:~0] when a phrase is missing | * after four letters | History expires after 8 hours idle |
| Scopus | OR, W/n and PRE/n, AND, AND NOT | "" loose, {} exact | * | Curly quotes can break a query |
| OpenAlex | Capitals; none means AND | "" exact; ~N for nearness | * and ?, three letters | Searches full text too |
| Google Scholar | Not on its help page | Quotes around a title | Not on its help page | Help covers author:, quotes and Advanced search |
| EdCitation Find sources | AND, OR, NOT in the box | "As one exact phrase", "In the title only" | Not documented | Free, no account; names the index that answered |
Google Scholar's thin documentation
Google's Scholar help page documents the author: operator, quotation marks around a paper's title, and an Advanced search by author, title, publication and date (Google, n.d.). It says nothing about AND, OR, NOT or truncation. The Edinburgh guide calls Scholar a good starting point without the complex searching of a library database, and when Gusenbauer and Haddaway (2020) tested 28 search systems, Scholar accepted strings of at most 256 characters. Use it for citation chaining, as the guide to finding sources fast describes. Web of Science is not in the table: its help pages asked for a browser check on 2 October 2026 and could not be read.
How do I build a search string for a literature review?
Turn the question into concepts, give each concept a bracket of synonyms joined by OR, and join the brackets with AND:
- Split the question. "Do interventions reduce test anxiety in university students?" has three concepts.
- List words for each. Edinburgh's checklist: synonyms, related terms, spelling variants, terms that changed over time, abbreviations, technical terms.
- Bracket each concept with OR, and join the brackets with AND.
- Quote phrases and truncate stems long enough for the database.
- Leave NOT out, or run the search with and without it and read what disappeared.
- Test the phrases in EdCitation's Find sources with and without Match my words, and check that papers you already know turn up.
- Translate for each database: braces in Scopus, field tags in PubMed.
- Save the string exactly as run, with the date and the count.
The worked string:
("test anxiety" OR "exam anxiety" OR "examination anxiety") AND (student* OR undergraduate* OR "higher education") AND (intervention* OR therap* OR program*)
Check the string before you trust it
The PRESS guideline is the checklist for peer review of electronic search strategies. McGowan et al. (2016) kept six elements: translation of the question, Boolean and proximity operators, subject headings, text-word terms, spelling, syntax and line numbers, and limits and filters. Read your string against all six. The glossary defines Boolean operators and truncation.
How do I record searches for a systematic or scoping review?
Follow your review's published reporting guideline, and record as you search. For a systematic review that is PRISMA-S, whose 16 items include each database with its platform, every strategy copied and pasted exactly as run, the date of the last search and the records from each source (Rethlefsen et al., 2021). A scoping review reports to PRISMA-ScR, with 20 essential items and 2 optional ones (Tricco et al., 2018). Read them at source, and see our guides to systematic reviews and scoping reviews.
PubMed's history expires after eight hours idle, so save each strategy to your own file the moment it runs. The documented search for a systematic review runs in the databases your protocol names; Find sources is for scoping the question and testing phrases first.
What does Match my words do in EdCitation's Find sources?
Match my words narrows a search to your exact wording. In the filter panel of EdCitation's Find sources, it offers two tick boxes, "In the title only" and "As one exact phrase", and the line "AND, OR and NOT also work in the search box." For testing whether a phrase does its job, it is the best tool we know: about 300 million published works, nothing to look up first, free with no account, and every result a record that exists, never one written for you, which no chatbot can promise.
What came back on 2 October 2026
Each search ran at Best match, five seconds apart, and each was answered by OpenAlex, the index named under the results.
| Search in Find sources | Results | First result |
|---|---|---|
| test anxiety | 1,976,440 | Ray Hembree's 1988 paper on the correlates, causes, effects and treatment of test anxiety, Review of Educational Research, cited by 1,652 |
| As one exact phrase | 42,482 | The same |
| Both boxes ticked | 4,746 | The same |
| moral injury | 277,891 | Litz and colleagues' 2009 paper on moral injury in war veterans, Clinical Psychology Review, cited by 2,722 |
| As one exact phrase | 14,767 | The same |
| Both boxes ticked | 2,259 | The same |
The top barely moved; everything below it did, and sorting shows it. Sorted by Most cited, the loose test anxiety search opened with a 1994 paper re-evaluating the Life Orientation Test, a measure of optimism (cited 5,861 times), and its third result described a maze test of anxiety in rats. With As one exact phrase ticked, the same sort gave Hembree's paper, Cassady and Johnson's 2002 paper on cognitive test anxiety and academic performance, and a 1967 paper by Liebert and Morris, all on the subject.
Boolean in the search box
"moral injury" AND (nurse OR nurses OR nursing) returned 6,166 results, led by Hossain and Clatty's 2020 Nursing Ethics paper on nurses' moral injury during COVID-19 (cited by 283). Adding NOT veterans gave 4,271, and two of the first five left the first hundred: Fitzpatrick and colleagues' 2022 survey of 676 nurses in Ohio, and Mantri and colleagues' 2020 symptom scale for healthcare professionals. Neither is a study of veterans; since OpenAlex searches full text, a passing mention is likely enough. That is Cochrane's warning, in two papers.
Read each record, too. In all three test anxiety searches, Moshe Zeidner's 1998 book Test Anxiety: The State of the Art was labelled an article; Crossref's record for its DOI files it as a book. When the main index is busy, Find sources names any filter it could not apply.
What is free, and what is paid
Find sources, Cite a source and Verify references are free with no account: find a paper, build its reference from the publisher's record in APA 7, MLA 9, Chicago 18 author-date, Harvard, IEEE or Vancouver, then check the finished list. Pro, at $8 a month, adds References from a file, which checks every reference and matches every in-text citation to the list. Max, at $24 a month, adds the Library. EdCitation finds, cites and checks; the search, the reading and every word of the review are yours.
Quick questions
What are the three Boolean operators?
AND, OR and NOT. AND keeps records with every term, OR keeps records with any, and NOT removes records containing a term, which the Cochrane Handbook advises avoiding where possible.
Do AND, OR and NOT have to be in capitals?
In PubMed and OpenAlex, yes: both help pages ask for capitals. Typing them in capitals everywhere costs nothing.
What is the difference between quotation marks and braces in Scopus?
Straight quotation marks give a loose phrase that also finds plurals and spelling variants. Braces give an exact phrase, matched as typed.
Does Google Scholar support Boolean search?
Its help page does not say. It documents the author: operator, quotation marks around a title and the Advanced search fields, so test a Boolean string before relying on it.
Can I search an exact phrase in EdCitation?
Yes. In Find sources, tick "As one exact phrase" under Match my words, and add "In the title only" to narrow further. It is free and needs no account.
References
- Elsevier. (2026, August 24). How can I best use the Advanced search? Scopus Support Center. https://www.elsevier.support/scopus/answer/how-can-i-best-use-the-advanced-search
- Google. (n.d.). Google Scholar search help. https://scholar.google.com/intl/en/scholar/help.html
- Gusenbauer, M., & Haddaway, N. R. (2020). Which academic search systems are suitable for systematic reviews or meta-analyses? Evaluating retrieval qualities of Google Scholar, PubMed, and 26 other resources. Research Synthesis Methods, 11(2), 181–217. https://doi.org/10.1002/jrsm.1378
- Lefebvre, C., Glanville, J., Briscoe, S., Featherstone, R., Littlewood, A., Metzendorf, M.-I., Noel-Storr, A., Paynter, R., Rader, T., Thomas, J., & Wieland, L. S. (2025). Chapter 4: Searching for and selecting studies. In J. P. T. Higgins, J. Thomas, J. Chandler, M. Cumpston, T. Li, M. J. Page, & V. A. Welch (Eds.), Cochrane handbook for systematic reviews of interventions (Version 6.5.1). Cochrane. https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-04
- McGowan, J., Sampson, M., Salzwedel, D. M., Cogo, E., Foerster, V., & Lefebvre, C. (2016). PRESS Peer Review of Electronic Search Strategies: 2015 guideline statement. Journal of Clinical Epidemiology, 75, 40–46. https://doi.org/10.1016/j.jclinepi.2016.01.021
- National Library of Medicine. (n.d.). PubMed user guide. https://pubmed.ncbi.nlm.nih.gov/help/
- OpenAlex. (2026, September 19). Search. OpenAlex Help Center. https://help.openalex.org/guides/searching
- Penn Libraries. (2025, January 16). Using the library catalog: Search syntax. University of Pennsylvania. https://guides.library.upenn.edu/c.php?g=1396908&p=10332888
- Rethlefsen, M. L., Kirtley, S., Waffenschmidt, S., Ayala, A. P., Moher, D., Page, M. J., & Koffel, J. B. (2021). PRISMA-S: An extension to the PRISMA statement for reporting literature searches in systematic reviews. Systematic Reviews, 10(1), Article 39. https://doi.org/10.1186/s13643-020-01542-z
- Tricco, A. C., Lillie, E., Zarin, W., O'Brien, K. K., Colquhoun, H., Levac, D., Moher, D., Peters, M. D. J., Horsley, T., Weeks, L., Hempel, S., Akl, E. A., Chang, C., McGowan, J., Stewart, L., Hartling, L., Aldcroft, A., Wilson, M. G., Garritty, C., . . . Straus, S. E. (2018). PRISMA extension for scoping reviews (PRISMA-ScR): Checklist and explanation. Annals of Internal Medicine, 169(7), 467–473. https://doi.org/10.7326/M18-0850
- University of Edinburgh. (n.d.). Search effectively. Literature Searching Resources. https://edinburgh-uk.libguides.com/Literature_searching/search-effectively
- Utah State University Libraries. (2026, July 22). Boolean operators: Nesting, truncation & wildcards. https://libguides.usu.edu/c.php?g=955766&p=6898015