Searching is likely to be complex and involve multiple steps. Before you start, carefully consider what words you need to include in your search. Think about:
Consider using a combination of free-text words and subject headings/index terms when searching to help improve the accuracy of your search results.
It can be useful to record your search terms and search strings in Notepad or MS Excel. That way you can copy and paste your search into different databases easily and avoid any issues that might occur when you copy and paste from MS Word.
Look at the appendices of existing reviews for an idea of what's involved in creating a comprehensive search. See below for some examples of search strategies.
Search operators (also called Boolean operators) allow you to include multiple words and concepts in your searches. This means you can search for all of your terms at once rather than carrying out multiple searches for each concept.
There are three main operators:
This is a search derived from a systematic review titled: “Systematic review of risk prediction models for falls after stroke.”
See Search Example 1 (tab above) to view how this search was performed in the databases.
Content from Systematic Review Library guide, Royal College of Surgeons in Ireland Library. Reused and adapted here with their kind permission.
‘Systematic review of risk prediction models for falls after stroke’[1]
In the published review, searches were conducted on seven databases (Medline, Embase, CINAHL, PsychINFO, Web of Science, Cochrane Library and SCOPUS. In accordance with best practice the published review presents all search strings as executed on all databases as supplemental data.
The table below gives a summary search strategy for this topic for PubMed Medline in Advanced mode using a combination of keywords and Medical Subject Headings to conduct a comprehensive search.
| Aspect | Keywords | Subject Headings |
| Stroke/brain trauma | "stroke" OR "poststroke" OR "hemiplegia" OR "brain hemorrhage" | Cerebrovascular Disorders OR Cerebrovascular Trauma OR Stroke OR Brain Infarction |
| AND | ||
| Falls | "falls" OR "falling" OR "accident" OR "accidents" OR "slips" OR "trips" OR "tripped" OR "stumble" |
Accidental Falls OR Accidents |
| AND | ||
| Risk | "risk" OR "prediction" OR "predictive" OR "score" |
Risk OR Risk Assessment OR Risk Management |
Searches #1 AND #2 AND #3 are combined to give a final result
[1] Walsh ME, Horgan NF, Walsh CD, et al Systematic review of risk prediction models for falls after stroke J Epidemiol Community Health 2016;70:513-519.
Content from Systematic Review Library guide, Royal College of Surgeons in Ireland Library. Reused and adapted here with their kind permission.
‘Topical non-steroidal anti-inflammatory drugs for analgesia in traumatic corneal abrasions’[1]
OBJECTIVES: To identify and evaluate all randomised controlled trials (RCTs) comparing the use of topical NSAIDs with placebo or any alternative analgesic interventions in adults with traumatic corneal abrasions, to reduce pain, and its effects on healing time.
| Aspect | Keywords | Subject Headings |
| Randomized controlled trial | "Randomized" OR "Randomised" OR "Placebo" OR "Randomly" OR "Trial" OR "Groups" |
Randomized controlled trial |
| AND | ||
| Eye, Eye Injuries | "Eye" OR "Eyes" OR "Cornea" OR "Corneas" OR "injury" OR "injuries" OR "abrasion" OR "abrasions" OR "erosion" OR "erosions" OR "trauma" OR "traumas" OR "wound" OR "wounds" OR "foreign" |
Cornea OR Corneal Diseases OR Wounds and Injuries OR Eye Injuries |
| AND | ||
| Anti Inflammatory Agents | "Nsaid" OR "nonsteroidal anti‐inflammator" OR "non‐steroidal anti‐inflammator" OR "diclofenac" OR "fenoprofen" OR "flurbiprofen" OR "indomethacin" OR "ketoprofen" OR "ketorolac" OR "piroxicam" OR "bromfenac" OR "nepafenac" OR "oxyphenbutazone" OR "suprofen" |
anti inflammatory agents non steroidal OR diclofenac OR indometacin OR ketoprofen |
| AND | ||
| Analegsia | "Analgesia" OR "Pain" | Analgesia OR Pain |
[1] Wakai A, Lawrenson JG, Lawrenson AL, et al Topical non-steroidal anti-inflammatory drugs for analgesia in traumatic corneal abrasions. Cochrane Database Syst Rev. 2017 May 18;5:CD009781. doi: 10.1002/14651858.CD009781.pub2.
Content from Systematic Review Library guide, Royal College of Surgeons in Ireland Library. Reused and adapted here with their kind permission.
'Wound Cleansing for Pressure Ulcers' [1]
Identify and group the main keywords and subject headings
| Aspect | Keywords | Subject Headings |
| Wound cleansing | "Normal saline" OR "Povidone" OR "Water" OR "Soap*" | Solutions OR Alcohols OR Water OR Soaps |
| AND | ||
| Pressure Ulcers | "Pressure ulcer*" OR "Pressure sore" OR "Bed ulcer*" OR "bed sore*" OR "bedsore*" OR "Decubitus ulcer" |
Pressure Ulcer |
[1] Moore ZEH, Cowman S. Wound cleansing for pressure ulcers. Cochrane Database of Systematic Reviews 2005, Issue 4. Art. No.: CD004983. DOI: 10.1002/14651858.CD004983.pub2
Content from Systematic Review Library guide, Royal College of Surgeons in Ireland Library. Reused and adapted here with their kind permission.
Although databases have developed, and some will automatically search for variant spellings, mostly they will just search for the exact letters you type in. Use wildcard and truncation symbols to take control of your search and include variations to widen your search and ensure you don't miss something relevant.
A truncation symbol (*) retrieves any number of letters - useful to find different word endings based on the root of a word
africa* will find africa, african, africans, africaans
agricultur* will find agriculture, agricultural, agriculturalist
A wildcard symbol (?) replaces a single letter. It's useful for retrieving alternate spelling spellings (i.e. British vs. American English) and simple plurals
wom?n will find woman or women
behavio?r will find behaviour or behavior
Hint: Not all databases use the ? and * symbols, so check the online help screens before you start.
Video from University of Reading Library on literature searching tips and tricks
Jump to 01:45 for truncation and 05:46 for wildcards.
Sometimes your search may contain common words (i.e. development, communication) which will retrieve too many irrelevant records, even when using an AND search. On many databases, including Google, to look for a specific phrase, use inverted commas:
Your search will only bring back items containing these exact phrases.
Some databases automatically perform a phrase search if you do not use any search operators. For example, "agriculture Africa" is not a phrase used in English so you may not find any items on the subject. Use AND in between your search words to avoid this.
On Scopus to search for an exact phrase use { } e.g. {agricultural development}. Using quotes on Scopus will find your words in the same field (e.g. title) but not necessarily next to one another.
Some databases use proximity operators, which are a more advanced search function. You can use these to tell the database how close one word must be to another and, in some cases, in what order. This makes a search more specific and excludes irrelevant records.
For instance, if you were searching for references about women in Africa, you might retrieve irrelevant records for items about women published in Africa. Performing a proximity search will only retrieve the two words in the same sentence, making your search more accurate.
Each database has its own way of proximity searching, so it's important to check the online help before you start. Here are some examples of the variety of possible searches:
Methodological search filters are search terms or strategies that identify a topic or aspect. They are predefined, tried and tested filters which can be applied to a search.
Examples:
They are available to select via the results filters displayed alongside your results. For instance, on PubMed after running your results it is possible to limit by 'Ages' which gives predefined groupings such as 'Infant: birth-23 months'.
In a systematic review, you will need to keep the search as similar as possible between different databases. Each database is unique and has its own features and tools. You will need to adapt your strategy for each database depending on the searching options available on each one.
Keep a record of the searches you run on each database to help you develop your search and to include in your write up.
Look at the Help section of individual databases to find a user guide. Most databases have these and have all the information that you will need to tailor your search strategy for that database.
Should I search with MeSH alone or keyword or both?
You can search using both MeSH terms and keywords. Combining both approaches can yield more comprehensive results. Dundar and Fleeman (2017) report that students can find it difficult to decide on how best to combine search terms and indeed how many search/MeSH terms to include in their search strategy. The authors advise that combining keywords and MeSH terms is good practice but caution that the exact number of terms to use depends on the students review question and inclusion/exclusion criteria.
Note: Automatic Term mapping will not be applied to keywords contained within double quotations or keywords that are hyphenated or tagged.
Examples of searches using combined keywords and MeSH terms can be seen in Search Examples 1,2 & 3 in the tabbed box Putting Search Terms Together.
Dundar, Y. and Fleeman, N. (2017) 'Developing My Search Strategy', in Boland, A., Cherry, G. M. and Dickson, R., (eds.) Doing a Systematic Review: a students guide. 2nd ed. London: SAGE Publications Ltd., pp. 61-78.
CINAHL Subject Headings works in much the same way as MeSH. The CINAHL Subject Headings authority file is a controlled vocabulary thesaurus that assists in more effectively searching your CINAHL database. Each bibliographic reference in the database is associated with a set of subject terms that are assigned to describe the content of an article.
For a detailed look at searching with MeSH in Cochrane see the video below.
Note: Not all Cochrane records have MeSH terms assigned to them. Records indexed with MeSH include those gathered from PubMed (Medline) and ClinicalTrials.gov (a trials registry). CINAHL records and those added by hand searching do not have MeSH terms. It is therefore best to use both keyword and MeSH terms when performing a comprehensive search.
To try to ensure your strategy is retrieving all the relevant studies you can create a test set of records. This is a group of records you would want (and expect) your search strategy to retrieve. This set is usually decided by the reviewers or from the studies included in an earlier review.