Searching by topic
A. Starting your search: Developing keywords from a topic
To find resources on a topic you must craft a search strategy, which involves the following steps:
1. Break your topic down into its main concepts which will be your search terms (keywords).
Topic: the impacts of climate on the migration of butterflies
Concepts/Search terms: climate migration butterflies
Don't include common words such as "impacts," "effects," "role," "of," "on," or "the." These occur in almost every article and so won't help you to find the specific articles that are relevant to your topic.
2. Choose an appropriate database in which to begin your search. You may find that you need to use more than one database. Click on the link below for a descriptive list:
B. Building your search using AND, OR, and parentheses
- will retrieve results that include ALL of the terms
- should be used to join terms describing different concepts
- Example: migration AND butterflies
- This search will retrieve all article records that include both the term migration and the term butterflies.
- narrows a search to retrieve fewer results
- in most databases and search engines, including AND is optional. Terms separated by a single space will be searched as though they are separated by AND.
- Example: The following searches are interpreted in the same way by database search engines:
- climate migration butterflies
- climate AND migration AND butterflies
- will retrieve results that include ANY of the terms
- should be used to join terms describing related concepts or synonyms
- Example: climate OR temperature
- broadens a search to retrieve more results
- A common error: Using OR to join terms that don't express a similar concept will retrieve irrelevant results:
- Less effective: climate OR butterflies
- This search will retrieve all records that include the term climate (whether or not they have anything to do with butterflies) as well as all records that include the term butterflies (whether or not they investigate climate effects).
- More effective: climate OR temperature
- This search will retrieve all records that include either the term climate or the term temperature.
Parentheses: if you're using both AND and OR in your search, use parentheses to indicate to which terms the operators apply
- Less effective: climate OR temperature AND migration AND butterflies
This search will retrieve every record that includes the term climate, whether or not it has anything to do with the migration of butterflies, as well as every record that includes all the terms temperature, migration, and butterflies.
- More effective: (climate OR temperature) AND migration AND butterflies
This search will retrieve records that include either the term climate or the term temperature, but only when either term occurs with both the terms migration and butterflies.
A note on capitalizing AND and OR:
- OR is not "or": It's very important when you use the operators AND and OR that you capitalize all their letters. If you enter them in lower or mixed case many databases and catalogs will read them as the words "and" and "or," and will ignore them. The words "and," "or," "the," "is" and many other common words are known as "stop words" because databases and catalogs skip them when they are parsing the search string.
Implied ANDs: This can have major effects on your search. Many databases and catalogs use an implied AND: if two terms are not combined with a specified operator, AND is assumed. Thus, for many databases and catalogs the two searches on either side of the equals sign in the example below are considered equivalent:
So when you use a lower-case "or" and it is ignored, many databases and catalogs will insert an implied AND between the terms:
- Example: climate migration butterflies = climate AND migration AND butterflies
- (climate or temperature) and migration and butterflies =
- (climate temperature) migration butterflies =
- (climate AND temperature) AND migration AND butterflies
- Instead of searching for resources about the migration of butterflies that also contain either the term climate or the term temperature, the database or catalog will search only for resources containing all the terms, changing the results of your search.
C. Narrowing a Search
If you've retrieved too many irrelevant records, these strategies may be helpful in refining your search:
- Adding additional concept terms with AND (see Building a search above)
- Phrase searching
Enclosing two or more words in quotes will search for those words as a phrase.
A common error: Enclosing too many words in quotes. Only words that almost always occur together should be enclosed in quotes.
- Example: "climate change" will retrieve all records in which the words climate and change occur in direct sequence.
- Less effective:
- "primary production in tropical rainforests"
PubMed: Phrase searching turns off automatic term mapping in PubMed, and so is not generally recommended when you are searching that database.
- More effective:
- "primary production" AND "tropical rainforests"
- Applying limits
Most article databases provide options to limit searches by various criteria. In BIOSIS Previews, for example, it's possible to limit searches by:
All of these options are available in the "Refine Results" sidebar, which is visible in the results screen after you've done an initial search in BIOSIS.
- Document Type (article, book chapter, etc.)
- Literature Type (such as literature reviews... learn more)
- Major Concept (Ecology, Behavior, etc.)
- Taxonomic Data
D. Broadening a Search
If your search has retrieved too few results, these strategies may be helpful in retrieving more results:
- Adding synonyms or related terms with OR (see Building a search above)
You can broaden a search by using truncation to find different forms of a search term.
Truncation can be applied to more than one search term, if appropriate.
- Example: If migration is one of your search terms, you would want to retrieve articles that include the following forms of the term:
Find the last letter that is common to all of the different forms of the term, and after it place the wildcard character (in BIOSIS Previews and many other databases, an asterisk (*, or Shift-8)):
A common error: If you truncate incorrectly, you will either miss relevant results, or retrieve irrelevant results:
- migratory, etc.
Some words shouldn't be truncated:
- migrati* will miss migrate, migrated, migrates, etc., which are all relevant.
- migra* will retrieve migraine, which is irrelevant.
In these cases, using OR is more effective: (gene OR genes OR genetic OR genetics)
- gene* will find genetic and genes, but will also find general, generally, etc.
- ant* will find ants, but also anthropology, anthropological, anterior, etc.
PubMed: Truncation turns off automatic term mapping in PubMed, and so is not generally recommended when you are searching that database.
Google: Truncation is not recognized by Google websites (Google, Google Scholar, Google Books, YouTube, etc.).
E. Combining strategies
Here are the number of results retrieved by performing a topic search in BIOSIS Previews by combining these search strategies (the number of results is current as of 14 June 2022; the numbers will change with time as articles are constantly being added to the database):
||No. of results
climate AND butterflies
|Adding a new concept (migration) with AND:
climate AND butterflies AND migration
|Adding a related term (temperature) with OR:
(climate OR temperature) AND butterflies AND migration
|Truncating migration to retrieve other forms of the word:
(climate OR temperature) AND butterflies AND migrat*
|Truncating other keywords (if appropriate):
(climat* OR temperature*) AND butterfl* AND migrat*
("climat* chang*" OR temperature*) AND butterfl* AND migrat*