01 · The Question
What if older studies use population labels you would not use today?
The language used to describe people changes. Terminology may become more precise, communities may prefer different language, classifications may change, and labels once common in scholarly literature may become dated, stigmatizing, misleading, or otherwise inappropriate.
That creates a genuine information-retrieval problem. If older publications contain only the terminology used at the time, searching exclusively with contemporary language can fail to retrieve them. Yet reproducing outdated labels without explanation can make a search strategy look as though it endorses language included solely for historical retrieval.
The solution is to distinguish the vocabulary you use to find historical records from the language you use to describe people in your own research.
03 · What You Need to Know
Retrieval vocabulary and authorial vocabulary serve different purposes
Search strategies sometimes have to preserve the language of the literature
A bibliographic search cannot retroactively rewrite the titles and abstracts of older publications. If an eligible paper was described using a historical population label, that label may remain part of its searchable bibliographic record.
The NIH Library explicitly advises that terminology for populations, diseases, symptoms, and medical conditions evolves over time and that comprehensive searches may sometimes need outdated terminology to reflect those shifts.
This creates an important distinction:
Language used for retrieval
Terms included because they occur in historical records or indexing and may be necessary to find eligible evidence.
Language used by the researcher
The terminology you choose when describing populations, interpreting findings, and communicating your own research.
Including a historical term in a Boolean query does not require you to adopt that term in your narrative description of the population.
Why current terminology alone can miss older evidence
Suppose terminology changed substantially during the period covered by your review. Recent papers may use the contemporary label, while older titles and abstracts use terminology that has largely disappeared. Searching only the modern term can create a time-dependent retrieval gap.
The problem can also occur in database indexing. Subject headings change, preferred terms are revised, and older index terms may matter when constructing historical searches. The PRESS search-strategy checklist explicitly asks reviewers to consider whether relevant previous index terms are missing.
The farther back your search extends, the more important it can become to investigate how terminology changed over time .
Do not assume that every old label belongs in the search
Historical terminology should not become a miscellaneous collection of every expression ever applied to a population. A term is useful when there is a plausible retrieval reason for including it.
Look for evidence in:
known relevant older papers;
titles and abstracts from the relevant period;
older subject headings or thesaurus records;
historical reviews and reference lists;
terminology used in the disciplines represented in your review.
For a rigorous search, terms should earn their place through conceptual relevance or demonstrated retrieval value. This is also why knowing when you have enough synonyms for a concept is more useful than trying to make the longest possible list.
Separate outdated terminology from inaccurate terminology
Not every old expression is merely an obsolete synonym. Some labels reflect classifications or assumptions that no longer map neatly onto contemporary concepts. Others may group populations differently from current terminology.
This means that a historical term should not automatically be connected with OR merely because it was once used in approximately the same area.
Watch Out
A historical population label may have covered a broader, narrower, or conceptually different group from the population defined in your current eligibility criteria. Verify the historical meaning before treating the term as equivalent to a contemporary label.
If two labels have substantially different meanings, the issue becomes one of distinguishing genuinely different concepts , not merely updating vocabulary.
Current and historical free-text terms can work together
When the terms genuinely provide alternative routes to the eligible population, contemporary and historical expressions can be combined within the same population concept block using OR.
A simplified structure might be:
("current population term" OR "historical term A" OR "historical term B")
This is only a conceptual illustration. Real strategies may also require plural forms, spelling variants, abbreviations, truncation, proximity searching, and field restrictions. PRESS guidance specifically asks whether free-text searching adequately represents synonyms, spelling variants, acronyms, and other relevant forms.
When historical sources use abbreviations or variant spellings, the same logic applies to acronyms, abbreviations, and spelling variations : include them when they plausibly improve retrieval, not merely because they exist.
Controlled vocabulary can help, but inspect its history
Controlled vocabularies can normalize some variation by indexing records under standardized concepts. However, thesauri themselves evolve. Headings can be introduced, revised, replaced, reorganized, or interpreted differently across databases.
Do not assume that today's preferred heading has always been available or that every older record has been retrospectively indexed under it. Search-strategy quality guidance consequently treats previous index terms as something that may need explicit consideration.
Check the thesaurus or indexing documentation of the database you are actually searching. The relationship between free-text keywords and subject headings becomes especially useful when terminology has changed historically.
Historical terms may be necessary even when they are uncomfortable to reproduce
Some older labels are not simply unfashionable. They may now be regarded as stigmatizing, demeaning, pathologizing, or otherwise inappropriate. Their appearance in a reproducible search strategy can nevertheless be necessary when those exact expressions occur in eligible historical records.
The methodological reason should be explicit. A transparent note can explain that legacy terminology was included solely to retrieve literature published or indexed under historical language.
This is not quite the same problem as determining how to search when older terminology is now considered inappropriate . That issue deserves particular attention to the ethical and reporting implications. Here, the central problem is population retrieval across terminology change.
Consider the time span of the search
Historical terminology matters only insofar as it corresponds to literature you actually intend to retrieve. A review beginning in a recent period may have little need for terminology that disappeared decades earlier. A review extending much further back may require substantial vocabulary archaeology. Academic searching occasionally does resemble fieldwork, except the artifacts are thesaurus entries.
Before adding a historical term, ask whether it was in use during the years covered by your search and whether relevant records from that period are likely to contain it.
Test historical terms rather than assuming their value
Run candidate terms individually or in controlled combinations and inspect what they retrieve. A historical term may recover unique eligible records. It may also retrieve overwhelming quantities of unrelated material because its meaning was broad or ambiguous.
Search development is iterative. Search-methodology guidance recognizes that strategies are commonly refined through scoping and testing before being finalized.
If a term is highly ambiguous, database-specific techniques such as proximity operators or field restrictions may improve precision without sacrificing all of its historical retrieval value.
04 · A Practical Example
Searching a population across several generations of terminology
Hypothetical Example
A review includes literature published over several decades
Imagine that you are reviewing an educational intervention for a population whose accepted terminology has changed substantially over time. Your eligibility criteria are based on a contemporary definition, but the search extends back several decades.
Preliminary searching shows that recent publications use the current terminology. Several known eligible older studies, however, use historical labels in their titles or abstracts, and older indexing also differs from current practice.
Define Specify the population concept according to the eligibility criteria rather than according to any one historical label.
Trace Inspect known studies from different publication periods to identify terminology actually used for eligible populations.
Verify Determine whether each historical expression represented substantially the same eligible population at the time or a meaningfully different group.
Search Combine justified current and historical free-text expressions and inspect relevant database subject headings.
Test Check whether known older and newer eligible studies are retrieved and whether historical terms contribute unique relevant records.
Document Record that legacy terminology is retained for historical retrieval and does not represent the terminology adopted by the researchers.
This approach preserves historical discoverability without requiring the research team to reproduce outdated terminology as its own descriptive language.
06 · What This Means for You
Preserve historical discoverability without adopting historical language
When a review extends into periods in which populations were described differently, treat terminology change as part of search design. Begin from the population defined by your eligibility criteria, then work backward through the language used to represent that population in the literature.
Documenting why a legacy term appears is particularly useful when the search strategy will be published, peer reviewed, registered, or shared with collaborators.
A simple decision framework
If a historical term occurs in known eligible older studies
Consider including it as a retrieval term after verifying its historical meaning.
If the term represented a different population
Do not treat it automatically as a synonym simply because terminology later changed.
If your search covers only recent literature
Check whether the historical terminology is actually relevant to that publication period before adding it.
If the historical term is now considered inappropriate
Use it only when methodologically justified for retrieval and explain its historical search function where necessary.
If an old term retrieves mostly irrelevant material
Investigate more precise phrasing, proximity, fields, subject headings, or whether the term contributes enough value to retain.
07 · A Quick Checklist
Before using outdated population terms in a search
Check whether you have:
Defined the eligible population independently of any one historical label.
Examined older relevant records for terminology actually used during the period being searched.
Verified that historical terms refer sufficiently closely to the population defined in your eligibility criteria.
Checked previous and current subject headings in the databases you are searching where relevant.
Combined justified historical terminology with appropriate current terminology rather than replacing one with the other.
Tested whether historical terms retrieve unique relevant records.
Used contemporary appropriate terminology in your own narrative writing.
Documented the retrieval purpose of potentially sensitive legacy terminology when clarification is warranted.
11 · Cite this Guide
How to Cite This Guide
This guide is intended to be read, shared, and used in research, teaching, and academic work. If you draw on its ideas, explanations, or other content, please acknowledge the source by citing the guide. Doing so gives appropriate credit and helps your readers locate the original resource.
Recommended (Field Guide)
APA
MLA
Chicago
Copy Citation
