OR is used in two ways.
1. OR is used if there is more than one word or phrase for your topic.
Itching OR Pruritis
Sometimes an article will use decide to use one term instead of another even if they both mean the same thing. If you only search for “itching” you will exclude any articles that say “rash” instead.
2. OR lets you look at related topics at the same time.
Itching OR Pruritis OR Rash OR Hives OR Urticaria
Just because you itch doesn’t mean you have a skin disease, but some discussions that revolve around skin diseases can still apply to itching.
Let's say you want to look at Insects and Diseases overall. Start by listing Insects and Diseases separately.
Combine the two to see what counts as Insects OR Diseases.
Searching for Insects OR Diseases pulls everything involving Insects OR Diseases. That includes what they don't have in common like Depression because it is not a disease carried by insects and Butterflies because they do not carry diseases.
Using OR to search for alternative terms would be searching for "Insects OR Bugs" or "Diseases OR Illnesses".
When using OR for replacement terms, be sure to use parentheses to partition off the terms used. For example, if you want to search for diseases or illnesses caused by insects, use "insects AND (diseases OR illnesses)" not "insects AND diseases OR illnesses." The latter search will include all the results for "insects and diseases" and "illnesses," even those illnesses unrelated to insects.
Search for a topic (e.g. Cats or Itching) without using OR. Note how many results you get. Search for a topic that can be said in two different ways (e.g. Cats OR Felines or Itching OR Rash). Does the number of results increase or decrease?
Form a question based on two common topics. Search for one topic (e.g. Cats or Itching) without using OR. Note how many results you get and how relevant they are to your question. Search for both topics (e.g. Cats OR Dogs or Itching OR Skin Disease). Does the number of results increase or decrease? Are the results more relevant or less relevant?
Truncation searches for multiple variants of the same word by cutting
a word down to its stem and adding * to it.
Databases tend to be very specific with their searches. If you search for “medicine”, it pulls all of the articles that use that word. This unintentionally limits your search because the database doesn’t pull up any variants of that word.
Instead of searching for “medicine”, “medicines”, “medicinal”, “medicinally”, “medic”, “medical”, “medically”, and “medics” separately, truncation lets you search for all of these at the same time. In this case, you cut “medicine” into “medic” and add the * as a substitute for all of those other endings.
Entering medic* lets the database know that you are looking for all of the articles that use words that start with “medic”, expanding your results.
NOTE: If you used controlled vocabulary in PubMed to narrow your search, truncation will cause it to turn off its automatic mapping of your search terms to its controlled vocabulary. This will broaden your search, but may give you results that are not as related to your original search before using truncation.
Some other databases use the dollar sign ($) or the question mark (?) as truncation symbols.
If you are using an unfamiliar database, check its help screens or user guide to determine the appropriate truncation symbol.
Take the word "hear" and write * at the end of it. Next to it, think of all of the different possible words that start the same way but end differently.
Search for "hear" and note of how many results you get. Do the search again with * added at the end of it. How many results did you get that time? Are they just as relevant as when you used the just "hear"?
When searching using MeSH or subject headings, the explode function can help you expand your search if you've narrowed it too much.
Using dynamite to get through a mountain opens many new paths for you to travel. Similarly, when using subject headings to narrow your search, the explode function can broaden your search to include the subject chosen and all subheadings underneath it. PubMed automatically explodes your search, click here to see how to use explode in the CINAHL database.