Inclusion criteria are a set of predefined characteristics used to identify subjects who will be included in a research study. Inclusion criteria, along with exclusion criteria, make up the selection or eligibility criteria used to rule in or out the target population for a research study. Inclusion criteria should respond to the scientific objective of the study and are critical to accomplish it. Proper selection of inclusion criteria will optimize the external and internal validity of the study, improve its feasibility, lower its costs, and minimize ethical concerns; specifically, good selection criteria will ensure the homogeneity of the sample population, reduce confounding, and increase the likelihood of finding a true association between exposure/intervention and outcomes. In prospective studies (cohort and clinical trials), they also will ...