Questions About Cancer? 1-800-4-CANCER

Levels of Evidence for Human Studies of Cancer Complementary and Alternative Medicine (PDQ®)

Health Professional Version
Last Modified: 08/26/2010

Combined Level of Evidence Score

A combined level of evidence score is calculated for each qualifying study—except for Best Case Series—by joining the score for statistical strength of study design with the score for strength of the endpoint(s) measured. Because of their extremely weak study design, Best Case Series are given a score for strength of study design only (i.e., a level of evidence score of 4). The level of evidence scores for the remaining study types range, in decreasing order of strength, from 1iA to 3iiiDiii.