PPT Slide
Appraisal process: Levels of evidence
Level III
-non-randomized concurrent (contemporary) controls
Level IV
-non-randomized historical controls
Level V
-case series without controls
One of the basic assumptions of the Scientific Method is the underlying assumption that all research be designed to minimize the influence bias, including the scientist's own, on the outcome of an experiment.
Kuhn, Thomas. The Structure of Scientific Revolutions (Univ. of Chicago Press, 1962).