A Nurse Working on a Surgical Unit Is Committed to Basing

A nurse working on a surgical unit is committed to basing practice on evidence. As he reviews guidelines for the basis of a quality improvement initiative on the unit, he identifies recommendations that are based on the lowest-level evidence and decides that he will not include these recommendations in the current initiative. Which of the following is the lowest level of clinical practice evidence?

A) Opinions of authorities and/or reports of expert committees
B) Randomized controlled trials
C) Systematic review of descriptive and qualitative studies
D) Observational studies with controls
E) Single descriptive or qualitative study