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SML Research Guide

A comprehensive guide for any one interested in doing a literature search in the medical/health sciences fields.

The aim of this module is to provide general basic information that everyone should be aware of for efficient computer searching.

Searching efficiently any online database requires an understanding of the ABCs of searching that ensure a good knowledge about Boolean Operators, Truncation/Wildcard, and Phrase searching.

Boolean Operators

Boolean Operators 

There are three Boolean Operators: AND, OR, NOT. It is very important that you use the correct Boolean operator when combining concepts as shown below:


This retrieves records with both concepts A AND B present in the same record of each of the retrieved records.

AND decreases the number of hits retrieved form the search.


This retrieves records with both concepts A OR B  OR records with both (A AND B) to be present in the same record of each of the retrieved records.

OR decreases the number of hits retrieved form the search.


This retrieves records with only concept A in each of the retrieved records.

Be cautious for you might lose relevant results.

When more than two concepts are combined using different Boolean Operators, grouping (or nesting) should be applied. This is because some computer programs process Boolean "AND" before "OR", others process "OR" before, still others process strategy from left to right, and in each processing different results are achieved (shaded part below). To override this, grouping using parenthesis should be utilized.

                                                                                                                                                                                                                                      A AND (OR C)                                                                      (A AND B) OR C

Note: Some programs have a default Boolean like Google has AND as a default Boolean, so searching Google for mad cow is as if you are searching mad AND cow.
Grouping when applied overrides how the program processes the Boolean statement, so what is within the brackets are always processed first.  The above two examples retrieve different results as shown in the shades.

Truncation / Wildcard

Truncation is a useful option that can be utilized to retrieve better results and it can be either external or internal:


External truncation allows searching for all occurrences of words that start with a specific root. Medline(OVID) allows external truncation by using * at the end of the word to represent zero or more characters.

For example in Medline(OVID), mutagen* gives us: mutagen OR mutagens OR mutagenical OR mutagenic OR other word variations starting with "mutagen" without typing these keywords with the Boolean OR separating them.


Wildcard or Internal Truncation allows searchings for a predefined number of characters usually either zero or one character. Medline(OVID) allows internal truncation and wildcard by using which represents 0 or 1 character.

For example in Medline(OVID),

  • colo?r gives us: color OR colour,
  • wom?n gives us: woman OR women
  • hypothesis gives us: hypothesis OR hypotheses
  • kid? gives us kid OR kids,

without typing keywords with the Boolean OR separating them.

You are being efficient, you are saving time!

Phrase or Proximity/ Adjacency Searching

Phrase search is used to force retrieval of two or more words next to each other, that is appearing as a phrase.

Searching Google for instance for mad cow, will retrieve any of the hits with the words mad AND cow not next to each other. Like: "a mad man kicked a cow", " a mad cow kicked a man", "there was a mad crowd passing by the farm and they spotted a cow", etc.But if you are interested in mad and cow appearing next to each other with  no words in between use "mad cow" as a phrase.

Proximity/ Adjacency searching is used to force the database to look up words with a specific count of words next to them without ORing different phrases.

In each database, it is of different syntax, for more check here.

For example in Medline(OVID), nutritional adj1 disease gives me all the phrases listed below ORed:

  • diseases of nutritional
  • nutritional disease
  • nutritional or metabolic disease

It gives all phrases with maximum of "1" (in this case) word coming between the words nutritional AND disease interchangeably.There is no specific # next to adj, it depends on the number of results you want to retrieve, the more you want, the bigger the number becomes. But stay cautious concerning how far you want the words apart, the further they are, the more the less relevant the results would be.

Field Searching

Using field searching under advanced searches allows users search in any of the title of the articles OR abstracts OR textwords OR publication name OR publication place, or to search in combination of one or more.


To do a good search on any database, you should read the "help", "search tips", "how to search", "search guide" and check for the database in hand what of the Boolean Operators, Truncation, and proximity options is/are present and what is the syntax, and then apply in a logical way accordingly.

Remember, conducing a literature search is not always error free, the effectiveness of the search depends on:

  • expertise of the researcher in defining the topic precisely and which concept should be addressed more than the other
  • how specific and accurate is the indexing of the database you are using 

There is no single correct way to do every search! The same topic can be tackled form different perspectives by the same researcher of from another lens from another researcher.