Refers to empirical research that applies rigorous, systematic, and objective procedures to obtain valid knowledge. This includes research that employs systematic, empirical methods that draw on observation or experiment; has been accepted by a peer-reviewed journal or approved by a panel of independent experts through a comparably rigorous, objective and scientific review; involves rigorous data analyses that are adequate to test the stated hypotheses and justify the general conclusions drawn; relies on measurements or observational methods that provide valid data across evaluators and observers and across multiple measurements and observations; and can be generalized.