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An important part of all research and particularly of Evidence-Based medical research is carefully formulating your research question. It's much easier to find the information you're looking for when you take the time to outline your question. One formula for mapping out your question is PICO.
The PICO model will help you to construct your "foreground" clinical questions. Your question should address each of the following areas.
P patient/population/problem or condition
I relevant intervention, exposure or test that you want to use in relation to the patient/population or problem
C comparison (alternative) intervention, exposure or test, if there is one
O outcome, or what you are most concerned about happening
Positive Outcomes: Prevention of illness or improvement in health
Negative Outcomes: Side effects/Adverse effects
Once you have identified criteria for each portion of PICO, you can use those keywords in your searches.