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Systematic Reviews

An introduction to systematic reviews, with examples from health sciences and medicine

Search Strategy

These are two search lines for Sub-Saharan Africa research. 
The first line searches for primary concepts and 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.

Line Terms
1

sub-saharan africa or east* africa or west* africa or southern africa or central africa

2 Angola* or Benin or Botswana* or Burkina Faso or Burundi* or Cameroon* or Cape Verde* or Central African Republic or Chad* or Comoro* or Democratic Republic of the Congo or Congo* or Cote d'Ivoire or Djibouti or Equatorial Guinea* or Guinea-Bissau or Eritrea* or Ethiopia* or Gabon* or Gambia* or Ghana* or Guinea* or Kenya* or Lesotho or Liberia* or Madagascar or Malagasy or Malawi* or Mali* or Mauritania* or Mauritius or Mozambi* or Namibia* or Niger* or Nigeria* or Rwanda* or Sao Tome and Principe or Senegal* or Seychelles* or Sierra Leone* or Somalia* or South Africa* or Swaziland* or Sudan* or Tanzania* or Western Sahara or Togo* or Uganda* or Zambia* or Zimbabwe* 
3 1 or 2

Errors

1. Quotation Marks on Phrases

The strategy has an AND in the term Sao Tome and Principe and the phrase has not been delineated with quotation marks.  This changes the search to

((Angola* or Benin or Botswana* or Burkina Faso or Burundi* or Cameroon* or Cape Verde* or Central African Republic or Chad* or Comoro* or Democratic Republic of the Congo or Congo* or Cote d'Ivoire or Djibouti or Equatorial Guinea* or Guinea-Bissau or Eritrea* or Ethiopia* or Gabon* or Gambia* or Ghana* or Guinea* or Kenya* or Lesotho or Liberia* or Madagascar or Malagasy or Malawi* or Mali* or Mauritania* or Mauritius or Mozambi* or Namibia* or Niger* or Nigeria* or Rwanda* or Sao Tome) and Principe) or Senegal* or Seychelles* or Sierra Leone* or Somalia* or South Africa* or Swaziland* or Sudan* or Tanzania* or Western Sahara or Togo* or Uganda* or Zambia* or Zimbabwe*

Note the brackets around Sao Tome) and Principe)

This returns all of the country names up to Sao Tome only if the item also has Principe, however also includes all items containing the later country names.  It will therefore still be a large set of records including all items mentioning countries such as South Africa, Sudan and Zimbabwe but will have no items on countries like Kenya, Nigeria or Congo due to the error.  This is difficult to identify as the result set is still large and seems to have worked correctly.

Fix this issue by adding quotation marks around phrases containing OR, AND or NOT or other system commands.   For searches on the Ovid database platform the terms SUB, USE and ROOT are also command terms that require quotation marks.  "Sao Tome and Principe" and "sub saharan" should be used.  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. 

This is the most problematic error that can be introduced as it is does not return all of the search terms in a group.  Avoid this error first!

 

2. Over-use of Truncation

Many of the country names have been truncated to return their plural form and population groups.  Individual terms should be tested first before including a truncation in a combined list of terms such as this one.

Mali* returns malignant, malignancy and malignancies.   This changes line 2 from a search for African countries to a search for African countries and a significant proportion of cancer literature.   

Fix this issue by testing terms one at a time in the database before combining lots of them.  Mali* has more than 600000 items in Medline whereas Angola* has 2000 items.  It is evident there is an issue that needs investigating.  Search for the truncated term and individual terms you expect to retrieve and NOT one search from the other to investigate what other terms are retrieved.

1 Mali*

2 Mali or Malis or Malian

3 1 not 2

These errors can introduce thousands of irrelevant results to the final result and cause extra weeks or months screening unnecessary items. 

 

3.  Not Testing Individual Terms First

Terms often 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 it's 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.

To fix this issue, search for Guinea in a separate line excluding the other forms.

Guinea* not ("Papua New Guinea*" or "guinea pig" or "guinea pigs")

These errors can introduce significant numbers of irrelevant items to final results.  If you see lots of unrelated items in your final result set check for this issue.

 

4. Different terms as 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.  It is common in subject heading structures for terms to be reversed in this manner.

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. 

Adding exp "Africa South of the Sahara"/ as a separate line in Medline Ovid improves this search strategy significantly.

This error can impact on the results of the published review being taken as a good attempt to identify all relevant literature.  It's impact depends on how much literature is missed by not using the most appropriate subject term for the database.

 

5. Effect of Dashes

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.

To fix this search for "sub-sahara*" or "sub sahara*" or subsahara* 

This error will usually mean at least some relevant literature is missed.  Never assume a term is always entered one way or the other - researchers always use every variant.

 

6. Redundant terms

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

Niger* returns both Niger, Nigeria, Nigerian and Nigerians

Congo* returns Congo, Democratic Republic of the Congo, Congolese and Congo's

Guinea* returns Guinea, Equatorial Guinea and Guinea-Bissau

This has no impact but can result in your search strategy being hard to interpret with overuse of redundant phrases.

Search with Errors Avoided

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.

Line Search Terms
1 "sub-sahara*" or "sub sahara*" or subsahara* or ((east* or west or central or southern) adj2 africa)
2 exp "Africa South of the Sahara"/
3 Angola* or Benin or Botswana* or "Burkina Faso" or Burundi* or Cameroon* or "Cape Verde*" or "Central African Republic" or Chad* or Comoro* or Congo* or "Cote d'Ivoire" or Djibouti or Eritrea* or Ethiopia* or Gabon* or Gambia* or Ghana* or Kenya* or Lesotho or Liberia* or Madagascar or Malagasy or Malawi* or Mauritania* or Mauritius or Mozambi* or Namibia* or Niger* or Rwanda* or "Sao Tome and Principe" or Senegal* or Seychelles* or "Sierra Leone*" or Somalia* or "South Africa*" or Swaziland* or Sudan* or Tanzania* or "Western Sahara" or Togo* or Uganda* or Zambia* or Zimbabwe*
4 Mali or Malis or Malian
5 Guinea* not ("papua new guinea*" or "guinea pig" or "guinea pigs")
6 1 or 2 or 3 or 4 or 5