Systematic Reviews for Health Sciences and Medicine

Example - search for Sub-Saharan Africa

A researcher is looking for studies from sub-saharan Africa and uses the 2 search lines below in Medline (Ovid).

• The first line searches for primary concepts
• The second line searches for individual nations that make up the area
• The third line combines the search results. 

This appears to follow best practice but has a number of commonly seen errors that can reduce the value of a search strategy.

This search has 6 common search errors

• Phrases missing quotation marks
• Too much truncation
• Multiple word meanings
• Missing subject headings
• Dealing with dashes
• Search terms not needed

See below for the solutions to each of these.

 Phrases missing quotation marks

Problem:

• Sao Tome and Principe is not enclosed in quotation marks.
• This means the AND is interpreted as part of the search.

• Results will include the countries up to Sao Tome  (in yellow) only if the word Principe appears as well.
• Results will include all the later countries  (in pink).  This is a large set of records including countries such as South Africa, Sudan and Zimbabwe.
• This is difficult to identify as the result set is still large and seems to have worked correctly. 

Solution:

• add quotation marks around phrases containing OR, AND or NOT
  "Sao Tome and Principe"
• In the Ovid database platform the terms SUB, USE and ROOT are also command terms that require quotation marks
  "sub saharan"
• If in any doubt, add quotation marks to all phrases
• In most database systems including Ebsco, Web of Science, Scopus and Proquest, search lines with OR and phrases without quotation marks will result in failures. 
   

Too much truncation

Problem:

• Many of the country names have been truncated to return their plural form and population groups. 
• Mali* returns malignant, malignancy and malignancies,  key terms for cancer literature

Solution:

• Test terms one at a time in the database before combining lots of them. 
• Mali* has more than 600 000 items whereas Angola* has 2000 items.  It is evident there is an issue that needs investigating. 
• To identify other irrelevant terms, search for the truncated term and individual terms you are expecting
• Then remove the individual terms with NOT 

Multiple word meanings

Problem:

• Search terms may have multiple meanings. 
• In some cases, the other meanings are not relevant to other parts of the search and are therefore not a significant issue. 
• However, you should be aware of what impact each term could have and determine whether its alternative meanings could be eliminated. 
• Guinea* also returns guinea pig, a significant research animal, and Papua New Guinea, a country not within Sub-Saharan Africa.

Solution:

• Search for Guinea in a separate line excluding the other forms.
  Guinea* not ("Papua New Guinea*" or "guinea pig" or "guinea pigs")

Missing subject headings

Problem:

• This search does not include subject headings
• In Medline the subject heading for Sub-Saharan Africa is "Africa South of the Sahara"
• This term has narrower terms including regional terms "Africa, Central", "Africa, Eastern", "Africa, Southern", "Africa, Western" and a listing of all the countries in each region.  

Solution:

• To fix this, search for your concept terms with the Subject Heading Map function in the database you are using to check if alternative terms are used and see if there is a function to search for narrower headings at the same time. 
• In Medline (Ovid) you can explode a subject heading, meaning you can search for all the terms underneath
• Adding an exploded subject heading improves this search strategy significantly.
  exp "Africa South of the Sahara"/

Dealing with dashes

Problem:

• The search includes sub-saharan africa.  
• Phrases including dashes do not automatically search for variants that do not have the dash.  Usually a dash is treated as a space although when entered with quotation marks, forms with the space can be excluded.
•  In this case, sub-saharan refers to nothing other than Africa so Africa can be eliminated to return other phrases like sub-saharan population, sub-saharan nations or sub-saharan communities.

Solution:

• Include all variations within quotation marks.
  "sub-sahara*" or "sub sahara*" or "subsahara*" 

Search terms not needed

Problem:

• Terms that are included by themselves do not have to be repeated in phrases.
• This error doesn't improve the search but can simplify it in many cases.

Solution:

• Niger* returns both Niger, Nigeria, Nigerian and Nigerians
• Congo* returns Congo, Democratic Republic of the Congo, Congolese and Congos
• Guinea* returns Guinea, Equatorial Guinea and Guinea-Bissau

Search for Sub-Saharan Africa - revised

Here is an improved version for Sub-Saharan Africa for Medline (Ovid).  Searches in other databases would need an appropriate subject search in line 2.