What are randomized controlled trials (RCTs)? 

When looking at a study using a randomised controlled trial (RCT) design it can be useful to break down the research question using the PICO model:
Problem or Patient or Population of interest
Intervention of interest
Comparison of interest
Outcome(s) of interest
This model can be particularly useful when deciding on search terms for a literature search to identify papers on a particular clinical question.