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How to do a Literature Search: Using keywords

Combining your search terms

Having chosen your search terms, you next need to think about writing a search strategy to combine them in the most effective way.  There are three main commands used to do this: ANDOR and NOT.  These are sometimes referred to as 'boolean operators'.  Instead of searching for them as words, the database will interpret them as a command.

Using 'AND'

AND is used to combine different topic words so that all of the words must appear in the search results.

Add more keywords using AND to narrow down your search and find fewer results.  For example: boolean operator AND

Sunscreen AND Skin

Child AND Psychology

Using 'OR'

OR is used to combine similar topic words so that all of the words can appear in the search results.

Add more keywords using OR to broaden your search and find more results.  For example: boolean operator OR

Drug OR Medicine

Football OR Soccer 

Using both 'AND' and 'OR'

When using both 'AND' and 'OR in your search strategy, it is important to get them in the right order!  If you seach for:

Pregnancy AND Drugs OR Medicines

You will find articles covering pregnancy and drugs, but then everything in the database on medicines regardless of whether it is connected with pregnancy.  To avoid this, use brackets (parentheses): 

Pregnancy AND (Drugs OR Medicines)

This tells the computer to combine your synonyms (drugs/medicines) using 'OR' first, then combine with pregnancy.

Using 'NOT'

Most databases allow you to use NOT to exclude a term that you don't want to appear.  For example: boolean operator NOT

Zebra NOT Fish

But this should be used with caution.  For example:

Microgeneration AND power NOT USA 

Would exclude articles comparing microgeneration of power in the USA with the rest of the world.

boolean operators AND and NOT

Video: Boolean operators and search structure (05:32)