What Are Phrase Searching, Truncation, and Wildcards, and When Should You Use Them?

What Do Quotation Marks, Asterisks, and Wildcards Actually Do to a Search?

You have found the right concepts and collected useful search terms. Then the search strategy starts acquiring punctuation: quotation marks around phrases, an asterisk at the end of a word, perhaps a question mark or another symbol inside one.

These are not decorative additions. Phrase searching, truncation, and wildcards change how a database interprets the characters you enter. They can help you keep words together, retrieve several word endings from one stem, or account for spelling variations without listing every form separately.

They can also make a search worse. An unnecessarily restrictive phrase can miss relevant wording. An overly short truncation stem can retrieve large amounts of irrelevant material. A wildcard copied from another database may do something different or nothing useful at all.

The key is to match the technique to the retrieval problem rather than adding search syntax because a sophisticated search is supposed to look complicated.

Each Technique Solves a Different Search Problem

How Phrase Searching, Truncation, and Wildcards Change Your Query

Start With the Problem You Are Trying to Solve

These three techniques are often taught together because they appear in advanced database searches, but they do different jobs.

The terminology itself is not perfectly standardized across platforms. Some databases use wildcard as the general name for a symbol that also performs right-hand truncation. PubMed, for example, describes its asterisk as a wildcard that substitutes for zero or more characters and uses it for what researchers commonly call truncation.

For practical searching, the symbol's documented behavior matters more than the label attached to it.

What Is Phrase Searching?

A phrase search tells a database that several words should be treated together rather than independently, although the exact interpretation depends on the search system.

Consider:

Phrase searching can therefore improve precision when the meaning depends on words occurring together.

Useful candidates often include established multiword concepts, intervention names, diagnostic expressions, methodological terminology, organization names, and other expressions whose component words become much less specific when separated.

Phrase Searching Is Not Simply "Put Every Multiword Term in Quotation Marks"

A phrase can be too restrictive.

Suppose authors express the same concept as teacher professional development, professional development for teachers, and teachers' professional development. Searching only one exact phrase may miss the others even though all represent closely related language.

The question is therefore whether adjacency and word order are part of what makes the expression meaningful. If reasonable variations can occur between or around the words, an exact phrase may sacrifice useful retrieval.

When you need words to occur near one another without requiring a single exact formulation, proximity searching may be more appropriate than either a rigid phrase or a loose AND search.

Quotation Marks Do Not Behave Identically in Every Database

Double quotation marks are widely associated with phrase searching, but their exact consequences are platform-specific.

PubMed provides a useful example. Its current documentation states that double quotation marks can be used to bypass Automatic Term Mapping (ATM) and search a specific phrase. However, if the quoted phrase is not found in PubMed's phrase index, the quotation marks may be ignored and PubMed displays a warning that the quoted phrase was not found.

PubMed also notes that searching a phrase changes automatic MeSH behavior. A quoted phrase does not receive the same automatic mapping and hierarchical expansion that an ordinary unquoted query may receive.

PubMed's Phrase Index Creates an Important Exception

PubMed maintains a phrase index for phrase searching. If a phrase is recognized, quotation marks can force that phrase rather than allowing ordinary Automatic Term Mapping.

If the phrase is not in the phrase index, however, PubMed may ignore the quotation marks. Its current documentation recommends a proximity search with a distance of zero as one way to search an unrecognized phrase with the words adjacent to one another.

This illustrates a broader principle: visible syntax does not guarantee the behavior you intended. Check warnings, search details, and platform documentation when phrase searching matters to the strategy.

What Is Truncation?

Truncation searches a stable portion of a word while allowing additional characters to follow it.

A common conceptual example is:

The main advantage is efficiency. Instead of writing several closely related word forms with OR, one truncated stem may retrieve them together.

This can be particularly useful when you have already identified important spelling and word-form variations that share a suitable character sequence.

Truncation Broadens the Search

Unlike phrase searching, which often increases precision, truncation usually increases retrieval because more character sequences can satisfy the search.

That is useful only if the additional words remain relevant.

Consider a deliberately simplified example. If a researcher wants variants related to therapist and chooses a stem that is too short, the search may retrieve many words sharing those initial characters but representing other concepts. The database is doing exactly what it was instructed to do; the problem is that the chosen stem was insufficiently specific.

A good truncation point is long enough to avoid unrelated vocabulary but short enough to capture the useful endings.

Do Not Truncate Earlier Than Necessary

Suppose several relevant terms are:

• psychology
• psychological
• psychologist
• psychologists

You might look for a shared stem. But moving the truncation symbol progressively leftward can increase the number of unintended matches. The shortest possible stem is not necessarily the most comprehensive in any useful sense.

Test candidate stems. Run the truncated term by itself and inspect the vocabulary appearing in the results. If the search suddenly becomes dominated by unrelated words, move the truncation point to the right or use explicit alternatives instead.

Truncation Can Sometimes Capture Singular and Plural Forms

A term such as adolescent* might capture both adolescent and adolescents in a system where the asterisk represents zero or more following characters.

But explicit truncation may be unnecessary if the database already handles singular and plural forms automatically. PubMed, for example, may add singular/plural variants through its ordinary search processing, while using wildcards changes that processing.

Before truncating every noun, check whether the platform already retrieves the variants you need. Redundant syntax makes a strategy harder to read without necessarily making it more comprehensive.

What Is a Wildcard?

A wildcard is a symbol that substitutes for one or more characters according to the rules of the search platform.

Wildcards are particularly useful when variation occurs inside a word rather than only at its ending.

Consider British and American spelling:

This is where wildcard searching differs conceptually from ordinary right-hand truncation. The variable character can occur within the term.

Wildcard Terminology Varies Across Platforms

Do not assume that an asterisk always means truncation while a question mark always means a single-character wildcard.

PubMed currently uses an asterisk (*) as its wildcard symbol for zero or more characters. It permits multiple wildcards in a term, which means an expression such as organi*ation* can represent internal and terminal variation. PubMed requires at least four characters before the first wildcard.

Other database platforms may use different symbols or distinguish explicitly between truncation and single-character wildcards.

This is precisely why the same search syntax cannot be assumed to work across research databases.

Wildcards Can Capture Regional Spelling Efficiently

Regional spelling variation is a common use case.

PubMed's current documentation provides an instructive phrase example using wildcard patterns to capture both tumor and tumour as well as singular and plural forms of macrophage. This demonstrates that wildcards can sometimes replace several explicit OR alternatives with one compact expression.

The gain is not merely cosmetic. A well-designed wildcard can make a strategy easier to translate, audit, and maintain. But only if its behavior is understood and tested.

Wildcards Can Change Automatic Search Processing

Special syntax can have consequences beyond character matching.

In PubMed, wildcard searches turn off Automatic Term Mapping for the affected expression. They also prevent the automatic process that would otherwise include a mapped MeSH term and more specific terms beneath it in the MeSH hierarchy.

For example, PubMed states that a wildcarded phrase based on heart attack will not automatically map in the same way to the MeSH concept Myocardial Infarction and its hierarchical expansion.

This means that adding an asterisk can simultaneously gain lexical variants and lose automatic conceptual expansion.

These are different retrieval mechanisms. One should not be assumed to replace the other.

Phrase Searching and Truncation Can Sometimes Be Combined

Some platforms allow wildcards or truncation inside phrases.

PubMed, for example, currently permits wildcarded phrases such as "vaccin* schedul*". According to its documentation, this can retrieve phrase variations including forms corresponding to vaccine, vaccination, schedule, schedules, and scheduling.

This can be useful when the structure of a phrase is relatively stable but one or more of its component words vary morphologically.

Again, do not assume another database supports the same combination or syntax.

Phrase Searching Is Different From Proximity Searching

A phrase usually requires words to occur together in a tightly specified way. Proximity searching allows them to occur within a specified distance, often in either order depending on the platform.

Do not force a phrase merely because AND retrieves too much noise. If authors legitimately vary the word order or insert other words, proximity may better reflect the language of the literature.

Phrase Searching Can Improve Precision but Reduce Recall

Suppose the literature contains all of the following:

• professional development for teachers
• teacher professional development
• professional development of school teachers

An exact search for one formulation may be precise but incomplete. Searching the component concepts with AND may be more sensitive but much noisier. A suitable proximity operator, where available, may occupy the useful middle ground.

The appropriate choice depends on the variability of the terminology and the purpose of the search.

Truncation Can Improve Recall but Reduce Precision

The same trade-off operates in the opposite direction with truncation.

Adding a truncation symbol expands the number of character sequences that can match. If most of those additional forms represent the intended concept, recall may improve efficiently. If the stem generates unrelated words, precision deteriorates.

There is no universally correct amount of truncation. Test the term in the actual database and inspect the additional vocabulary it retrieves.

Wildcards Are Useful Only When the Variation Is Predictable

A wildcard works well when you know where characters vary.

If two terms are completely different, a wildcard cannot sensibly turn one into the other. Heart attack and myocardial infarction, for example, require alternative terminology rather than clever character substitution.

Wildcards therefore complement, rather than replace, the process of finding the different terms researchers use for the same concept.

Do Not Use Special Syntax Until You Know What It Adds

A search can become impressively cryptic while becoming methodologically worse.

Quotation marks, asterisks, question marks, field codes, Boolean operators, and parentheses all have legitimate purposes. Their accumulation is not evidence of rigor.

For each special operator, ask:

• What variation or ambiguity am I trying to control?
• What records should this syntax add or remove?
• Does this database support it?
• Does it disable or alter another search feature?
• Can I demonstrate that it improves retrieval?

If you cannot answer those questions, test the plain search against the modified version before keeping the syntax.

Search Details and Result Counts Can Reveal Unexpected Behavior

When the database provides a query translation or search history, use it.

PubMed's Advanced Search displays Search Details showing how a query was translated. It also issues warnings for problems such as phrases that were not found. Comparing searches with and without quotation marks or wildcards can reveal whether the syntax changed automatic mapping or retrieval in ways you did not anticipate.

Result counts alone do not prove that one version is better, but a dramatic change is a reason to investigate. Inspect relevant records unique to each version rather than choosing whichever query happens to return the more aesthetically pleasing number.

The Final Search Must Be Translated, Not Merely Copied

A phrase may transfer easily between databases while its quotation syntax does not. A truncation stem may remain conceptually useful while the truncation character changes. A wildcard may need a different symbol or may represent a different number of characters.

When searching several databases, preserve the retrieval intention:

This becomes especially important when you translate a search strategy from one database to another. What travels is the logic, not necessarily the punctuation.

How Do These Techniques Work Together in a Real Search?

That last step matters. Search syntax should make your concept representation better, not merely shorter or more elaborate.

Common Mistakes With Phrases, Truncation, and Wildcards

When Should You Use Each Search Technique?

Choose phrase searching, truncation, or wildcards only after identifying the specific linguistic problem you need to solve.

For a consequential search, test each technique independently before combining everything into the final query. If truncation adds useful variants, keep it. If quotation marks remove known relevant records, reconsider them. If a wildcard saves three OR terms without changing retrieval adversely, it may be worth using.

Search syntax should earn its place in the strategy in much the same way search terms do.

Before Using Special Search Syntax, Check How It Behaves

Frequently Asked Questions About Phrase Searching, Truncation, and Wildcards

Use Search Syntax to Solve a Specific Retrieval Problem

How to Cite This Guide

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