Proximity and phrase searching, and Boolean AND: 3 techniques to focus your literature search
Phrase searching and proximity searching are techniques that allow a researcher to control one word’s relationship to another in a literature search.
Phrase searching is widely known and widely used. It can be very helpful but has the potential to be a dangerous searching technique!
Proximity searching is related to phrase searching, and in fact encompasses it, but it casts a slightly wider searching net. Proximity searching can give your search the focus of a phrase search without missing relevant results you’ll want to see.
The Boolean operator AND is related to phrase and proximity searching because it requires search terms to appear in a record, but it does not control the relationship of terms to each other. Sometimes this is just what is needed for an excellent search.
Using the best technique for the concept you need to find will land you in the sweet spot for a search which is both efficient and comprehensive.
This blog post will help you understand these techniques — when to use them, when not to, and tricks to test if you are using the right tool at the right time.
Phrase searching means typing two or more words — words that, used together, capture a concept — inside quotation marks in a search.
Putting the words inside quotation marks instructs the search platform to return only those results which have the words together, in the order they were typed, with no words between them. The phrase needs to appear in the same database record field too, so for instance in the title or the abstract.
Using phrase searching can help eliminate false hits. Sometimes a phrase really is needed to capture a concept. “Public health” and “living wage”, for example, are phrases that need both words to convey their meaning.
It is extraordinarily easy to make a phrase out of words that do not need to be a phrase to capture a concept.
Say you’re searching for information on meat quality. Searching for “meat quality” will, indeed, bring back many results focused on the quality of meat, but it will not pick up many results that are equally focused on meat quality but do not have the two words right next to each other. Amongst the multitude of results this search would miss are:
- quality attributes of meat
- meat and burger quality.
- quality of a meat product
- meat safety and quality
Unless a phrase is a true phrase, other approaches are better for focusing a search. One possibility is using the Boolean operator AND to add an additional concept to the search. Another is using a proximity operator.
Tip: To check if a phrase is appropriate or not, try running your search as an AND combination NOT the phrase combination. Then scan the results to judge whether the non-phrase results are relevant or not. For meat quality the search would look like this:
(meat AND quality) NOT “meat quality”
Where can you use it? Almost everywhere. Phrase searching works in search engines and on most database platforms.
Important to know: Some search interfaces will treat words you type together as phrases whether or not you type the quotation marks. Ovid does this.
Tip: To check how a search interface is handling your search terms, run a two-word search. First, run it without quotation marks. Then run the same search with the words inside quotation marks. Compare the number of results for the two searches. If the number is the same for both searches, the platform is treating your search like a phrase even without the punctuation.
Proximity searching lets you determine how close one search term must be to another in order for the results to be useful for you.
Sometimes search terms need to be in each other’s vicinity to capture the idea you are looking for. Terms within five words of each other might still be quite directly related to each other but lose that relational meaning if they are in sentences at opposite ends of an abstract.
How close together terms need to be depends on the concepts and context. Beautifully, proximity operators let you judge exactly how close together your terms need to be.
Proximity operators are what you type between your search terms to run this type of search. Exactly what you type as a proximity operator is platform dependent. What they all have in common, though, is that they let you include a number to indicate the maximum distance the search terms can be separated from each other.
The operators for some commonly used platforms include:
EBSCOhost: Nn, Wn
How they work:
Nn (N standing for Near) n= number of words that one search term can be, in any order, from the other
Wn (W standing for Within) n= number of words that terms can appear from each other, but only in the order they were typed in the search
Example search: biodegradable N5 packaging
Sample results from the search:
- biodegradable packaging
- packaging film based on biodegradable
- biodegradable nitric oxide-releasing nanocellulose-chitosan packaging
Example search: biodegradable W1 packaging
Sample results from the search:
- biodegradable packaging
- biodegradable active packaging
Web of Science: NEAR/n
How it works: n=number of words, in any order, that one search term can be from the other
How it works: n=number of words that one search term can be, in any order, from the other
ProQuest: NEAR/n, PRE/n
How they work:
NEAR/n n= number of words that one search term can be, in any order, from the other
PRE/n n= number of words that terms can appear from each other, but only in the order they were typed in the search
Scopus: Pre/n, W/n
How they work:
W/n (Within) n= number of words that one search term can be, in any order, from the other
Pre/n (Preceding) n= number of words that terms can appear from each other, but only in the order they were typed in the search
If you look at the results from the example searches, you’ll notice that proximity search results always include the search words as phrases. However, they are also pulling back results where the sense of the phrase is retained even with some words appearing between the search terms.
Notice, too, that there is almost no uniformity between operators across platforms. Even the exact same operators can be assigned different meanings — on EBSCOhost W/n means that the terms must appear in the order typed, but on Scopus, W/n lets the terms appear in either order, while Pre/n keeps the terms in order.
All search platforms provide guidance on their proximity operators. You’ll find it in the embedded help pages: just search them for “proximity.” Consult the guidance to learn exactly what you need to do to get the best from these techniques on each platform.
Where can you use it?
Proximity searching works on most database hosting platforms including Ovid, EBSCOhost, ProQuest, and Web of Science. It also works on Scopus and Cochrane. It is not an option for search engines or PubMed.
Sometimes when you use a proximity operator, you will notice that your search has returned results where your terms are further apart (in terms of the number of words) than you indicated they should be.
This is not because the database search is messing up. Instead, it is due to stopwords. Stopwords are words that are not counted as words for a database’s search rules. They are usually common words, like and, as, for, from, is, of, that, the, this, to, was, and were.
Stopwords are also ignored if they are typed as search terms, which explains why PubMed has a very long list of stopwords even though you cannot use proximity searching on the platform. You should be able to find a list of stopwords for each platform you are using in its help section.
Know how to finetune your search
If we compare three search techniques — proximity searching, phrase searching, and the Boolean operator AND — we can see that between them these techniques offer researchers a full spectrum of control over how loose or tight the relationship between search terms is.
Knowing how to use all of them will enable you to finetune a search to exactly the right degree of focus.
Both search terms must appear in the record, but can appear anywhere in the record including in different fields unless a single field is specified.
Both search terms must appear in the record in the same field in whatever relationship is specified by the operator.
Both search terms must appear in the record in the same field next to each other in the order they have been typed.
Many researchers know about and regularly use ANDs and phrase searching. Consider investing a little time in mastering proximity searches, too. Doing so will give you a lot more control over your searching. A good proximity operator can give a search the focus of a phrase search without accidently missing completely relevant literature because a phrase turned out not to be a true phrase.
The more techniques you know, the easier you will find it to pull out the best option for any given search!
Finally, a note on language
Sometimes you’ll hear adjacency searching also talked about with proximity and phrase searching. Understanding the exact difference between the three terms can be confusing, because:
- Proximity searching and adjacency searching are sometimes used interchangeably to mean that two words searched with an appropriate operator between them can appear with either word in front, no more than a specified number of words apart from each other.
- But sometimes adjacency is used to mean that the words must appear in the same order they were typed in the search, no more than a specified number of words apart from each other.
- Then again, sometimes adjacency searching is used interchangeably with phrase searching to mean that two or more search terms must appear next to each in the order typed with no other words between them.
- Phrase searching is a kind of proximity searching. However, they are usually talked about as separate techniques.
Don’t worry too much about the language. Instead, focus on what the platform in front of you will let you do, and which techniques will open the door to the best results for your searching needs.