The Healthy People 2020 evidence-based resources identified have been selected by subject matter experts at the U.S. Department of Health and Human Resources. Each of the selected evidence-based resources has been rated and classified according to a set of selection criteria based, in part, on publication status, publication type, and number of studies. This classification scheme does not necessarily consider all dimensions of quality, such as statistical significance, effect size (e.g., magnitude of effect), meaningfulness of effect, additional effect over control, and study design (e.g., sample size, power, internal validity, external validity, generalizability, potential biases, potential confounders).