One of the great classic introductions to critical assessment of medical research is Trisha Greenhalgh’s series in the British Medical Journal ‘How to read a paper’. Although the practical aspects of critiquing a paper are better served by newer tools like CASP, Greenhalgh’s work has stood the test of time and is still worth recommending.
The best place to start is with ‘Getting your bearings — deciding what the paper is about’, and then have a look at ‘Assessing the methodological quality’, and ‘Statistics for the non-statistician I’ & ‘II’.
"It usually comes as a surprise ... to learn that some (perhaps most) published articles belong in the bin, and should certainly not be used to inform practice." — Trisha Greenhalgh.
