Reviewing scholarly literature – making a synthesis of various results, points of views or approaches – is an important task that one undertakes when writing a thesis. Reviewing and synthesizing will require you to gather the most relevant and authoritative literature for your research topic. In turn, finding relevant literature will depend on how well you know your field and the tools of discovery. The following routines will help you:
Although much information, including scholarly publications, is openly available on the Internet, the majority of the scholarly resources you will need are subscription-based. These are made available to you by your library.
Click the links to get an overview of the databases accessible at your institution. The lists of databases are organized both alphabetically and by subject. They are accessible from everywhere on campus. When you are off campus, check with your institution to find out how you can connect through proxy or VPN technology.
Visit your library home page and get acquainted with the services offered, such as courses and guidance in literature searching and reference management.
“I use bibliographies of other books a lot. If I have a good book that is related to what I’m doing, then I always carefully read the bibliographies.” PhD student, social sciences
Tracing references is an efficient way of identifying relevant literature for your doctoral thesis. References connect present findings with other findings and put pieces of knowledge into a wider context. Cited or citing documents allow us to follow a debate or development of a subject over time. Scholarly databases, such as Web of Science, Scopus and Google Scholar, are designed for tracing citations. These services give information on how often a document has been cited and by whom. How frequently a document has been cited is often associated to its impact and uptake in the rest of the research community. You can use features in these so-called citation databases to:
Not all databases, in particular book catalogues, incorporate citation networks. Some may however provide statistical information of usage, such as counts of clicks and downloads. Usage measures may give you hints about the impact of a specific document and help you to figure out trends or directions in a particular research area, and might in this way be helpful in your discovery.
Established researchers often follow their favourite journals or publishers in order to remain updated on their topic. When you have identified the commonly read journals or top publishers in your field, you may utilize their:
However, you should be aware that by following only certain journals or publishers you may miss a wider perspective. Due to the complexity of the publishing landscape, milestone papers may be, and in fact are, published through unexpected channels. Keep in mind that you may also need to look beyond your own field to discover multidisciplinary or cross-disciplinary research.
Literature databases, publisher- and journal websites, research blogs and social networks all provide newsfeeds (RSS) and research activity alerts which help you keep updated on recent research publications and developments in your field. Look for the following options:
Depending on the purpose of your literature search, you have the opportunity to search the web and/or the scholarly databases provided by your academic library. When your purpose is to identify the seminal literature of your field, search engines such as Google Scholar can offer convenient features to provide you with an initial overview. However, when your aim is to do a thorough search, you need to search specialized bibliographic databases. Diligent use of both options will enable you to conduct a rich discovery of the literature in your field.
Search engines increasingly provide scholarly content. They may be excellent for an efficient retrieval. In particular, Google Scholar offers a convenient, simple entrance. The service also provides links to your library holdings and information about citing documents within both Google Scholar itself and Web of Science. However, remember that
Not posted on the web
Not linked to and therefore not captured by a crawler
Placed beyond paywalls
Hidden in databases
Located within private sites of organisations, governments and companies
Not found because of your personal settings
Listed beyond the first pages
I consider it extremely important to be as in touch with the literature as possible of course. PhD student
In contrast to search engines, bibliographic databases have a different scope both in regard to the subject covered and the functionality implemented. In addition to basic bibliographic information, they may include abstracts, full texts, citations and other valuable descriptors of content. Bibliographic databases typically add value by supporting systematic searching and by providing further sources.
Databases offer a variety of options such as filtering and sorting, widening or narrowing, and specific search techniques like applying wildcards, quotation marks, operators and parentheses.
A long list of search results may be hard to browse and evaluate. Sorting and/or filtering the list might be useful.
Sort results by:
Filter results by:
You can define your searches so as to recall as much of the relevant literature as possible, known as high sensitivity, or to be very precise and to ensure high relevance, often called high specificity. Depending on your need, you can use the following approaches to
There are more specific search options to support your particular needs. Familiarize yourself with:
Wildcards help you include alternative spellings or word forms. This is useful when you search for several words with the same root or want to search for both the singular and plural form of a word. Wildcards are one of the most common features in databases. Frequently used wildcard characters include *,?, #, $. These characters have slightly different meanings; check the precise definition within the database. Here are three possible examples:
Example 1: Including alternative spellings or word forms
child* matches children, child, childhood, childish
Example 2: Some databases allow you to use a wild card at the beginning of the word to include variations.
*oxide yields peroxide, sulphoxide, nitroxide.
Example 3: Wild cards may also been used to replace one or several characters in your search word. This is useful, for example, when there is a difference in spelling between British and American English..
Colo?r matches both color and colour.
When you search for a specific phrase, enclose the phrase inside double quotation marks (“…”). This narrows your search to those exact words in that specific order.
Examples: “United Nations”, “breast cancer”
Boolean operators: The use of AND, OR and NOT, called Boolean logic, helps you to combine your search words. See detailed visualization.
Combining keywords with AND will retrieve a search result with all your search words included.
Example: influenza AND “vitamin C”
Combining keywords with OR will retrieve at least one of your search terms. This is useful when you want to include synonyms or related terms and are interested in either of the words.
Example: influenza OR “common cold”
Combining keywords with NOT will exclude search words from your result. Use this with great caution, as you do not necessarily have control of what is excluded from the result.
Example: “common cold” NOT “vitamin C”
In addition, you may combine earlier performed searches, which the database keeps track of.
Search 1: influenza OR “common cold”
Search 2: “vitamin C” OR garlic OR antibiotics
Search 3 : Search 1 AND Search 2 (which combines Search 1 and Search 2)
Proximity operators: Some databases help you search for words that are close to each other. Examples of this follow:
Web of Science
NEAR = Near operator. Add a number to define how many words may separate your search words.
Example: tax NEAR/5 reform, returns hits containing the words tax and reform within a five-word distance
N = Near operator. Retrieves hits containing the words regardless of the order in which they appear. Add a number to define how many words may separate your search words.
Example: tax N5 reform, finds records containing the words tax reform as well as reform of income tax.
W = Within Operator. Retrieves records with the words in the order you entered them. Add a number to define how many words may separate your search words.
Example: tax W8 reform, finds records containing tax reform but not reform of income tax.
ADJ = Adjacent operator. Retrieves records with the words regardless of the order in which they appear. Add a number to define how many words may separate your search words.
Example: tax ADJ4 reform, retrieves tax reform as well as reform of income tax.
By enclosing your search terms in parentheses, and using Boolean and proximity operators you can combine several keywords and build complex search expressions. Remember that expressions in inner parentheses are executed first.
Example: ((common cold) OR influenza) AND (garlic OR vitamin* OR (Antiviral treatment))
The records in a bibliographic database have attributes such as author, title, publisher, year, topic, methods. Using these attributes may help you develop a more efficient and targeted search strategy.
Title: Functional analysis / Walter Rudin
Author: Rudin, Walter
Printed: New York : McGraw-Hill
ISBN: 0-07-054236-8, 0-07-100944-2
Subjects: Mathematics | functional analysis
When you search for a document by a specific author, be aware that author names are presented in different ways across databases. Names might not be given in their full form; for instance, they may be presented with last name and initials only and will therefore only be searchable as such.
For a most complete result, a good strategy is to search for all possible name variations. Use wildcards to include different types of spelling.
Topic information is typically found in titles, abstracts, and keywords or subject headings. Using keywords that describe your topic is an efficient way of searching. This kind of searching is often referred to as text word searching.
You should note that different keywords are used to describe the same phenomena, and conversely, the same keywords may be used to describe very different phenomena. You will therefore need to think about relevant synonyms when searching. Using a thesaurus or subject heading will help you do this.
Some subject-specific databases maintain a controlled, hierarchical vocabulary to support your search. Searching the controlled vocabulary from a thesaurus is useful because it covers synonyms, related, broader and narrower keywords.
Make the remaining list of retrieved documents as relevant and precise as possible, get acquainted with the database that serves your area of interest and check whether you may apply specified filters for narrowing your search. You may, for example, filter your search by
In this section we present some examples of how searching in different databases can be performed. Experiment with the examples and become familiar with the various strategies for efficient searching.
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.
Date of search: 6.January 2014
Divide your search into several steps. Identify the main concepts in your research question and search separately for relevant keywords for each concept. In our example we take Self-esteem, adolescent, and divorced parents to be main concepts. Individual searches are then combined. You can then consider using various possibilities to refine your search result.
Step 1: Searching for self-esteem
Make sure to include various spelling and relevant synonyms of a search term or search concept. Check the thesaurus for possible subject headings that match your main search terms well enough to be included as search criteria. The thesaurus of a database may not have a Subject Heading that corresponds with your free text search terms. You will need then to consider whether or not any of the options available would be meaningful to include in your search. In PsycINFO a Subject Heading search will be marked with a slash (/) in the search history. Recall your search history to get an overview of the individual searches representing the main concept “self-esteem” and combine them using the Boolean operator OR. The list below shows search expressions and number of results in parentheses.
Search 1: self-esteem.ti,ab. (33648)
Search 2: selfesteem.ti,ab. (51)
Search 3: self esteem/ (20666)
Search 4: Search 1 OR Search 2 OR Search 3 (37436)
Step 2: Searching for adolescents
Truncating behind the ‘n’ in adolescen* will include adolescent, adolescents and adolescence. Truncating behind the ‘n’ in teen* will include teens*, teen-ager/-s and teenager/-s.
Search 5: adolescen*.ti,ab. (160146)
Search 6: teen*.ti,ab. (15288)
Search 7: adolescent development/ (30756)
Search 8: Search 5 OR Search 6 or Search 7 (171826)
Step 3: Searching for divorced parents
Truncating behind the ‘e’ in divorce* will include divorced (and therefore also “divorced parents” and “parents who are divorced”). Including terms other than divorce might be a good idea if it is not an important point that there has been a marriage before the break-up of the parents’ relationship. Remember to use quotation marks to delimit a compound search term. 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. (14081)
Search 10: “broken home*”.ti,ab. (503)
Search 11: “parent* breakup”.ti,ab. (7)
Search 12: “parent* break-up”.ti,ab. (9)
Search 13: divorce/ (7164)
Search 14: Search 9 OR Search 10 OR Search 11 OR Search 12 OR Search 13 (15255)
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 (94)
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 Methodology and mark the following options: 0800 Literature Review, 0830 Systematic Review and 1200 Meta Analysis. Limiting our research question by these types of applied methodology returns two documents.
Search 16: limit 15 to (0800 literature review or 0830 systematic review or 1200 meta analysis) (2)
For our research question The impact of having divorced parents on self-esteem in adolescents, a total of 94 documents were retrieved (Step 4) using PsycINFO on 06 January 2014. For an initial check of relevance of the retrieved documents, try browsing titles, year of publication, contributing authors and journals involved. Keep revising your search strategy and also consider setting up an alert. As no database is exhaustive, consider including searches in other databases.
Research question: Symbiotic relationships between Lepiotaceaean fungi and leaf-cutter ants.
Database: BIOSIS Previews, which is a part of Web of Knowledge. Relevant for the Life Sciences.
Date of search: 10. January 2014
Divide your search into several steps, search separately for relevant keywords according to your problem, combine and refine afterwards.
Step 1: Searching for leaf cutting ants and Lepiotaceaean fungi
Make sure to include various spellings and relevant synonyms of a search term or search concept. In this case, Latin names as well as 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 expressions 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 lepitoacae*) (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 summarize 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)
For our problem Symbiotic relationships between Lepiotaceaean fungi and leaf-cutter ants, a total of 385 documents were retrieved (Step 2) using BIOSIS on 10 January 2014.
While it is tempting to include a third search concept, symbiosis, this would exclude the documents dealing with symbiosis but without mentioning it in the title, abstract or keywords. If a paper already addresses both fungi and ants, it is also likely to relate to symbiosis.
For an initial check of relevance of the retrieved documents, try browsing titles, year of publication, contributing authors and 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.
Research question: The effectiveness of light therapy interventions to treat winter depression.
Database: PubMed (Medline). Relevant in biomedicine, life sciences and social sciences.
Date of search: May 2013
Divide your search into several steps and combine results afterwards. For searching literature in medicine and health, make use of defined subject headings in MeSH.
Step 1: Searching for winter depression
The MeSH term for this is seasonal affective disorder. In Scandinavia this condition is commonly named winter depression, which is mentioned in a few abstracts. They are all combined with OR, to retrieve articles where either of the phrases is mentioned. The list below shows search expressions and number of results in parentheses. Searches are marked with the hash symbol ( # ) in PubMed.
Search 1: seasonal affective disorder[MeSH Terms] 1039
Search 2: seasonal affective disorder[Title/Abstract] 976
Search 3: winter depression[Title/Abstract] 240
Search 4: #1 OR #2 OR #3 1414
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 words in title or abstract here add a few relevant articles. They are all combined with OR, to retrieve articles where either word is mentioned.
Search 5: phototherapy[MeSH Terms] 25680
Search 6: phototherapy[Title/Abstract] 4834
Search 7: light therapy[Title/Abstract] 1050
Search 8: #5 OR #6 OR #7 27496
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 #8 656
Step 4: Limiting search results
Now you have 656 references to articles concerning your search terms. If you want to decrease that number further, you can limit by study design, for example to reviews, which will result in 131 studies
Search 10: (# 9) Filters: Review 131
An additional limit by publishing year will decrease the number even further. There are 42 reviews published in the last ten years.
Search 11: (# 9) Filters: Review; published in the last 10 years 42
For an initial check of relevance of the retrieved documents, browse titles, year of publication, contributing authors and journals involved. Keep revising your search strategy and also consider setting up an alert. As no database is exhaustive, consider including searches in other databases. Pubmed is often used for finding needed clinical information. If you plan a systematic review, we advise you to search MedLine (Ovid).