Search Strategies

(Figure inspired by: White, R. W., & Roth, R. A. (2009). Exploratory search: Beyond the query-response paradigm (No. 3). Morgan & Claypool Publishers.)

Although locating relevant literature is always vital, in many cases it would be hardly possible, nor particularly meaningful, to attempt to capture “everything” that could shed light on a topic. The searching process is therefore often more exploratory, evolving and playing a constructive role throughout the process.

Searching often starts out exploratory, then gradually becomes more focused as one’s insight into a topic increases. Exploratory Searching typically involves a broader set of approaches, aimed at giving overview and insight into the existing body of relevant literature.

Berry Picking

The Berry Picking approach involves scanning results from brief searches and browsing for bits of information to discover new areas for examination. This approach is especially suitable for unfamiliar topics, since it allows the search process to evolve as the need for information changes. The process often involves a combination of simple Keyword Searching, Citation Tracing and nowadays, in many cases, also AI-based Semantic Searching.

Pearl Growing

The Pearl Growing technique is often a natural progression of the Berry Picking approach. Here, highly relevant identified records (the “pearls”), are used to trace and find more similar records. This can involve searching for known relevant sources (i.e., Look Up Search) and find similar literature through backward and forward Citation Tracing, Shared Citation Tools, Similar Article Tools or even AI-based chatbots. This approach is also highly useful when developing a Structured Search, since you can explore the identified records for relevant Keywords and Thesaurus Terms. The identified “pearls” can also serve as a control at a later stage, to check if a developed Structured Search is working properly (i.e., satisfactory recall).

Look Up Search

In many cases, you may want to check details in a source that you already know exist. You might for example want to read a source more carefully before citing it or you might want to check a fact or detail. For this type of searches, simply googeling the exact title might offer a quick solution. If you have more specific bibliographic information available, using the advanced search mode in a subject relevant database, where you can enter details like author name, journal title, volume, issue number or page number, can also be a useful approach.

Structured Searching remains a central element in literature reviews where a comprehensive and reproducible coverage of the relevant literature is important. The term Systematic Search is sometimes used when referring to especially exhaustive structured searches typically required in comprehensive reviews like Scoping Reviews and Systematic Reviews, where recall of virtually all relevant literature on a specific topic is sought by searching in multiple relevant databases – often supplemented by “hand searching” in especially relevant journals, citation tracing from relevant sources and searching for “grey literature”.

The process of developing a structured search involves various steps – here, we present a model that involves seven main steps.

Step 1: Question - Formulate the research question

The first step involves specifying the topic as a clearly formulated research question. The question should be as basic and specific as possible, while still capturing the essence of your topic.
Let’s say that your topic revolves around how chocolate and cocoa-based products consumption can affect the sense of happiness among people. This could be stated as a question as illustrated in the example above.

Step 2: Identify - Find the optimal search concepts 

The next step is identifying the most central concepts based on the stated research question. When identifying candidate concepts, it is important to focus on main concepts/elements that maximize the probability of finding the relevant literature. Suitable candidate concepts are typically the ones that are the most Specific Concepts and Important Concepts.

Specific concepts

 

Specific concepts: Terms like “chocolate” and “happiness”, in our example, are promising candidates for main concepts/elements, since they are quite specific/distinct. Terms like "does", "consumption", or even "people", are less suitable, because they are quite general and frequently used throughout much of the literature.

 

Important concepts

 

Important concepts: Terms that are highly likely to be mentioned in the title, abstract, or as author keywords, are considered Important and valuable. In our example, "chocolate" and "happiness" should be considered Important, since relevant literature on this topic is very likely to mention these, or related terms, in the title, abstract, or among the author keywords. Although "people" could also represent a candidate concept in our example, it is less Important, since it can be considered implicit that "chocolate" and "happiness" involves "people". Many literature records may therefore not necessarily mention “people” explicitly in the title, abstract or author keywords.

 

The ideal concepts for a structured search are both specific and important (i.e., highly likely to be mentioned in the title, abstract, author keywords) and thus situated in the top right corner area in the two-dimensional illustration above, where specificity and importance represents the two dimensions. In our example, "Chocolate" and "Happiness" are clearly the most ideal candidate concepts for a structured search on the topic. The combination of both low importance and specificity means that "People" should be discarded as candidate concept.

Step 3: Explore – Map synonyms and related search terms

As part of a structured search, it is useful to construct a concept table, as illustrated above – one column assigned to each main candidate concept – where you try to list all the terms that should be searched as synonyms or related terms.

To find relevant Keywords, it can be helpful to check the range of terms that are often used in fields like the title, abstract and author keywords of relevant records. Even more alternatives can often be found by asking AI-based chatbots (e.g., ChatGTP, Copilot), or by consulting synonyms or alternative entries listed for relevant Thesaurus Terms. In addition to keyword terms, the concept table should also include any relevant Thesaurus Terms from Bibliographic Databases you plan to search.

Some important considerations for selecting search terms are listed below:

Step 4: Mini searches - Build separate mini searches for each concept

Start in a Bibliographic Database that is central to the topic and supports building complex search strategies based on combining search lines from the Search History. Create a separate mini search for each concept listed in the Concept Table as illustrated above. 

Start with the fist concept and search each of the listed search terms – one at a time. It is recommended that you specify the search fields for each searched term – the most central fields are usually Title and Abstract (and author keywords if available). If the relevant databases also support Thesaurus Searching, these should be searched using the Thesaurus field (see line 5 and 6 in the example above).

When all the relevant terms for a specific concept have been searched for, complete the mini search by marking/selecting all the related search terms in the “search history” (i.e., line 1– 6 in the example above), and combine them using the OR operator (see line 7 in the example above). Repeat the process for each candidate concept.

Step 5: Complete the initial search

Complete the initial search by selecting/marking the mini searches for each concept (i.e., line 7 and 14 in the example above), and combine them using the AND Operator (see line 15 in the example above).

Step 6: Improve the search

Inspect and evaluate the literature identified in your initial search. Some important considerations include:

Step 7: Adjust to other databases

Decide what other Bibliographic Databases to include in the final search and make the necessary adjustments (e.g., wildcards, proximity operators, thesaurus terms). The number of required databases varies depending on the purpose. It is generally recommended to search in at least two that are complementary to each other, but Systematic Reviews, and other types of comprehensive knowledge overviews, may require searching in all the central subject specific databases. Minor adjustments of the search may be necessary due to different availability of various search fields, alternative Thesaurus System and different use of Truncation, Wildcards or Proximity Operators.

Save the search in the different databases and copy the final search history into a document, in case you need to modify or document the search at a later stage. 

Example: Medicine

Research question: Are light therapy treatments effective against winter depression?

Database: PubMed (Medline). Relevant in biomedicine, life sciences and social sciences.
 

Divide your search into several steps and combine results afterwards. When searching literature in medicine and health, make use of subject headings in the MeSH thesaurus.

Step 1: Searching for “winter depression”

The MeSH term for this is seasonal affective disorder. In Scandinavia, this condition is commonly called winter depression, which is mentioned in a few abstracts. The terms are combined with OR to retrieve articles in which either is mentioned. The list below shows search terms[field searched] and numbers of results. Searches are marked with the hash symbol ( # ) in PubMed.

Search 1: seasonal affective disorder[MeSH Terms] 1215
Search 2: "seasonal affective disorder"[Title/Abstract] 1264
Search 3: "winter depression"[Title/Abstract] 281
Search 4: #1 OR #2 OR #3 1744

Step 2: Searching for “light therapy interventions”

The correct MeSH term for light therapy intervention is phototherapy and this is combined with light therapy in the title and abstract as a synonym. Additional searches for the terms in titles or abstracts here add a few relevant articles. They are all combined with OR to retrieve articles in which either term is mentioned.

Search 5: phototherapy[MeSH Terms] 41845
Search 6: phototherapy[Title/Abstract] 8512
Search 7: "light therapy"[Title/Abstract] 2093
Search 8: #5 OR #6 OR #7 45782

Step 3: Combining search results

Finally, both sets of terms are combined with AND. This will retrieve a combination of the words above.

Search 9: #4 AND #8 771

Step 4: Limiting search results

Now you have 771 references to articles concerning your search terms. If you want to further decrease that number, you can limit the result, for example by study design. Reviews summarise previous research and may be a good starting point. In this case, by limiting to reviews, you will retreive 162 studies.

Search 10: (# 9) Filters: Review 162

In addition, limiting by year of publication will reduce the number of studies even further. There are 35 reviews published in the last ten years.

Search 11: (# 9) Filters: Review; published in the last ten years 35

Example: Biology

Research question: How is the symbiotic relationship between Lepiotaceaean fungi and leaf-cutter ants?

Database: BIOSIS Previews, which is a part of Web of Science. Relevant for the life sciences.

Divide your search into several steps; search separately for relevant keywords according to research topic; combine and refine afterwards.

Step 1: Searching for leaf cutter ants and Lepiotaceaea fungi

Make sure to include various spellings and relevant synonyms of a search term. In this case, Latin names and common names are combined in a Boolean OR search. Add a wildcard  (here *) to the stem of a word to include all forms. In BIOSIS, searching by topic means searching by title, abstract or keywords. The list below shows search terms and number of results in parentheses.

Search 1: Topic=(Atta OR Acromyrmex OR ("leaf cutt* ant*") OR ("leafcutt* ant*")) (1529)
Search 2: Topic=(fungus OR fungi OR lepiotaceae*) (488401)

Step 2: Combining search results

Go to your search history and combine the previous two searches with the Boolean operator AND. Searches are marked with the hash symbol (#) in BIOSIS.

Search 3: #1 AND #2 (385)

Step 3: Refine results to type of work

The left panel in the result list of the search interface lets you refine your search. Reviews summarise previous research and may be a good starting point. Choose Literature Types and tick off Literature Review if you would like to start with the eight papers retrieved in our example.

Search 4: Refined by: Literature Types=(LITERATURE REVIEW) (8)

Conclusion:

For our topic Symbiotic relationships between Lepiotaceae fungi and leaf-cutter ants, a total of 385 documents were retrieved in BIOSIS(Step 2).

While it is tempting to include a third search concept, symbiosis, this would exclude the documents dealing with symbiosis without mentioning it in the title, abstract or keywords. If a paper is about both fungi and ants, it is also likely to relate to symbiosis. In other words, this might increase the specificity of the search, but at the same time reduce the sensitivity.

For an initial check on the relevance of the retrieved documents, try browsing titles, year of publication, contributing authors and the journals involved. As no database is exhaustive, consider including searches in other databases. Keep revising your search strategy and also consider setting up an alert.

Example: Psychology

Research question: The impact of having divorced parents on self-esteem in adolescents.

Database: PsycINFO (Ovid). Relevant for psychology, health sciences, social sciences and education.

Divide your search into several steps. Identify the main concepts in your research question and search separately for relevant keywords for each concept. In this example, the main concepts are self-esteem, adolescents, and divorced parents. Individual searches for main concepts and synonyms / alternative spellings of search terms within a main concept are combined. You can then consider using various possibilities to refine your search result.

Step 1: Searching for “self-esteem”

Make sure to include various spellings and relevant synonyms of a search term or search concept. You might want to consider whether the concepts “self-respect” and/or “self-confidence” ought to be included. Many databases treat the spelling alternatives “self esteem” and “self-esteem” identically. It is recommended that you check if both alternatives need to be included. It is also easy to test whether a search term consisting of more than one word should be delimited with quotation marks.
Check the thesaurus for possible subject headings that match your main concepts well enough to be included as keywords. In PsycINFO (on Ovid), a subject heading search will be marked with a slash (/) in the search history. The Search History in the database presents the individual searches representing the main concept, “self-esteem”, and you combine them using the Boolean operator OR. The list below shows spelling variants of “self-esteem”, field searched (ti,ab = title, abstract), and the numbers of results in parentheses.

Search 1: self-esteem.ti,ab. (41932)
Search 2: selfesteem.ti,ab. (83)
Search 3: self esteem/ (24471)
Search 4: Search 1 OR Search 2 OR Search 3 (46039)

Step 2: Searching for adolescents

Truncating after the "n" in adolescen* will include adolescent, adolescents and adolescence. Truncating after the "n" in teen* will include teens, teen-ager/-s and teenager/-s.
You might also want to consider including the search terms youth*, “young people” and student*.

Search 5: adolescen*.ti,ab. (220286)
Search 6: teen*.ti,ab. (20825)
Search 7: adolescent development/ (45687)
Search 8: Search 5 OR Search 6 or Search 7 (236189)

Step 3: Searching for divorced parents

Truncating after the "e" in divorce* will include divorced (which will also identify “divorced parents” and “parents who are divorced”). Including terms other than divorce might be a good idea if it is unimportant that the parents were married before they broke up. PsycINFO allows for truncation within a compound search term, such as “parent* breakup” which will include parental breakup, parents breakup and parent breakup. The searches representing the concept of “divorce” are combined with OR (Search 14).

Search 9: divorce*.ti,ab. (16833)
Search 10: “broken home*”.ti,ab. (528)
Search 11: “parent* breakup”.ti,ab. (10)
Search 12: “parent* break-up”.ti,ab. (15)
Search 13: divorce/ (8244)
Search 14: Search 9 OR Search 10 OR Search 11 OR Search 12 OR Search 13 (18194)

Step 4: Combining search results

Go to your search history and combine previous searches with the Boolean operator AND.

Search 15: Search 4 AND Search 8 AND Search 14 (106)

Step 5: Refining results to type of work

You can refine your search by choosing Additional Limits. If, for example, you want to identify the reviews among your search results, choose the Methodology box and mark the following options: 0800 Literature Review, 0830 Systematic Review, 1200 Meta Analysis and 1300 Metasynthesis. Limiting our research question by these types of applied methodology retrieves 3 documents.

Search 16: limit 15 to (0800 literature review OR 0830 systematic review OR 1200 meta analysis OR 1300 metasynthesis) (3)

Conclusion

For our research question “The impact of having divorced parents on self-esteem in adolescents”, a total of 106 documents were retrieved in PsycINFO (Step 4) . Keep revising your search strategy and consider setting up an alert. As no database is exhaustive, consider including searches in other databases.

Example: Education

Research question: What is the teacher's role in supporting play in the kindergarten?

Database: ERIC (Ebsco). International database on education literature and resources.

Divide your research question into several concepts, search for them separately, and make use of the search history to combine results afterwards. When searching for literature in a database that has its own thesaurus, remember to make use of relevant thesaurus terms, also called subject headings.

Step 1: Searching for “kindergarten teacher”

When typing "kindergarten teacher" into the thesaurus, we learn that "Preschool teachers" is the correct subject heading. Therefore we first apply that in the field Descriptors [exact] (DE).

When searching the fields Title and Abstract (and Author keywords when available) - both “Kindergarten” and “Kindergarden” can be used, as well as “Preschool”, “Daycare”, “Child care center” and “Nursery”.

In search 2, each of these terms is combined with the Boolean operator OR, to retrieve articles where either is mentioned. They are then combined with a proximity operator (N8), saying that the word “teacher” should be found within 8 words' distance. All the words end with an asterisk, opening for any character following. For instance, nurser* includes nursery and nurseries. The same search string is used in the fields Title (TI), Abstract (AB), and Keywords (KW). Each string is enclosed within parentheses, which are combined with OR.

Then we combine Search 1 and Search 2 with OR. 

Step 2: Searching for “Play”

The thesaurus term is “Play”. Other terms like: Role Play, Playground activities may be considered, but are not included here.

We would also like to find articles with “Play” in the title, abstract or author keywords. We add an asterisk (*) to include different variations of the word (plays, played, playing), and again we search for the same thing in different fields, which we then combine with OR.

Step 3: Combining search results

Finally, both sets of terms are combined with AND. This will retrieve a combination of the words above.

Step 4: Limiting search results

Now you have 1755 references to articles concerning your search terms. If you want to decrease that number, you can limit, for example by study design or year of  publication. Limiting to references from 2018–2021 will retrieve 292 studies.

Conclusion

For an initial check on the relevance of the retrieved documents, browse titles and abstracts. Look for any other relevant search terms. Keep revising your search. When you are satisfied with the search, consider saving it and setting up an alert. As no database is exhaustive, also consider performing searches in other databases.

Library support for structured searching

For further input and advice on systematic searching, consult your library help pages on databases and literature searching. Some libraries offer courses in systematic searching, and some may even offer to provide such searches for you on request.

Saving and Rerunning Searches

Saving searches can help you avoid unnecessarily repeating searches you have done earlier. You can also edit and re-run searches if you have saved them.

To save the searches you have performed, and any document records that you want to keep for later, you need to register and create a profile in the database. Registering will also allow you to set up alerts to let you know when new results matching your queries appear. Think carefully about how you do this. It can be useful and time-saving to have the technology work for you and feed you new articles within your research area, but if you have too many alerts it may quickly become a source of distraction and frustration, rather than inspiration.

Keeping a Log of Your Searching Activities

Even though you may find many of the automatized functions in resources used for searching convenient and time-saving, you should also keep a personal record of your searching activities. If you make a note of the databases you have searched, the search strategies used, the dates of the searches, the results you retrieved, and the challenges encountered, you will likely avoid becoming frustrated over duplication of effort. Also, in certain cases (e.g., scoping- or systematic reviews, knowledge summaries), you will be required document the search process in detail.

Reference Management Tools

All the different resources used for searching also have functionality for exporting references to reference management tools. Some databases let you export references directly to your reference management tools, while others require that you first receive an email with the references. It is a matter of personal preference where and how you share, store and organise your references. However, we recommend using a reference manager.