Tip#67 Subject Areas in Scopus May Amplify the Noise in Your Search

The crux: 

In Scopus, pay attention to Subject area on the search results page to see if your search retrieves an unexpected number of records from non-relevant areas.  This is especially important when you include acronyms in a search. 

The multidisciplinary nature of Scopus presents opportunities and challenges. This post focuses on one of the challenges - records that contain your terms but are wildly irrelevant. This is referred to as noise in a search. Scopus's subject area feature can alert you to noise in your search and provide clues to which terms are causing it. 

On the left side of the Scopus results page, are options for refining the search. This is where you find the feature called Subject area. But it may not work how you think.  

Journal titles are classified in Scopus using its ASJC (All Science Journal Classification) scheme, a list of 361 numerical classification codes that correspond to subject areas. Classification is performed by in-house experts at the time Scopus coverage is established for a journal title and is based on its aims, scope, and published content. Subject areas are super-grouped under four branches of knowledge - life sciences, physical sciences, health sciences, and social sciences & humanities. Subject area classifications are assigned to journal titles and not to individual records. When a record appears within one or more subject areas, it is based on the journal in which that article is found. Often, journal titles are assigned more than one classification code. Thus, there is redundancy in record distribution across subject areas. 

Scopus subject area classifications

Recently, I received a literature search request where the investigator was interested in deep brain stimulation as an intervention for several psychiatric diseases including bipolar disorder. I crafted this simple search for Scopus:

TITLE-ABS-KEY ((deep-brain-stimulation OR DBS) AND (anxiety OR depression OR bipolar))

Surprisingly, the search string returned more records from non-medical disciplines than medical, which I discovered by checking the Subject area section of the Refine search options on the left side of the results page. An examination of records from non-medical subject areas indicated DBS, the acronym for deep brain stimulation, was causing some of the noise. In fact, additional testing showed a search for DBS in the abstract field retrieves ten times more records (600K vs 60k) from non-medical subject areas compared to medical! 

Upon further investigation, I found that most of the irrelevant records contained db and dbs in the abstract field. Scopus was interpreting the acronym DBS as the plural form of the abbreviation db signifying decibel.  In other words, the search was retrieving both singular and plural forms of the abbreviation for decibel - db and dbs. The concept of decibel has many applications in non-medical areas, but its plural abbreviation also happens to be the acronym for deep brain stimulation. DBS in the search was correctly retrieving records on deep brain stimulation and retrieving just as many irrelevant records related to decibels. DBS was the noise in the search. 

Results by subject area for search of DBS in abstract

But it wasn't the only noise. Bipolar was also present - with or without DBS - in many of the unwanted abstracts. 

So, I tested a search on bipolar alone in Scopus's title, abstract, keyword combination field, which also resulted in records substantially and widely represented in non-medical subject areas. As I soon learned, bipolar is a term with distinct meanings across many disciplines - from electronics to geography to mathematics to medicine. The term bipolar was retrieving both relevant and irrelevant records - thus it too was causing noise in the search. 

Results from TITLE-ABS-KEY (bipolar)

Even in medically focused databases like MEDLINE and Embase (both via Ovid), there are a number of subject headings with non-psychiatric meanings of the term bipolar that may cause noise in your search, but you'll have to scroll through search results to find irrelevant records as there is not a feature comparable to Scopus's subject. 

Non-psychiatric subject headings in MeSH & Emtree for bipolar:

• bipolar electrocautery 
• bipolar electrosurgical electrode (endoscopic) 
• bipolar forceps 
• bipolar neuron 
• bipolar transurethral resection 
• retina bipolar cell

Scopus subject areas makes it easy to investigate where noise resides in your search. Web of Science, also a multidisciplinary database, provides similar functionality via its Categories feature and is also located in the left side of the results page. 

That's all I've got.