As I mentioned in my previous post, scientific studies (e.g. experimental v. observational design) have different strengths and weaknesses. Sources of evidence range from case reports at the lower end to well-designed large randomized experimental clinical studies that minimize bias.  Relying on poor quality evidence can lead to policy decisions that aren’t in patients’ best interests- and it’s super important to figure out the actual “weight of evidence” that published studies provide- so public health can make good evidence-based decisions. 

That’s where the Grading of Recommendations Assessment, Development and Evaluation- or GRADE system comes in.  The GRADE system was developed to provide researchers and policy makers a systematic way of grading the strength of studies to help policy makers in medicine and public health to interpret studies and make better decisions.  The GRADE system has all kinds of applications.  For example, the U of A used the GRADE methodology to evaluate the quality of the studies looking at the benefits and harms of using Cannabis to treat the conditions that were petitioned to add to the list of qualifying conditions for a medical marijuana card.

You can read alot more about the GRADE system and how it works in this article in the British Medical Journal (unfortunately you need to pay to read the whole thing).