With the explosion of evidence based guidelines there have been a large number of ways of describing the quality of evidence behind the recommendations offered. Faced with the current multiplication, a guideline user may be faced with the same recommendation which is classified “II-2, B”, “C+, 1”, or “strong evidence, strongly recommended”, depending on which system is used. Is there an easy way of understanding them? What do they mean anyway?

Most systems have the same basic methods at their heart. The guideline developers are first asked to assess the methodological quality of the studies which …