All clinical research studies have a series of requirements that must be met; these are known as inclusion/exclusion criteria. Inclusion criteria allow certain persons to participate. Exclusion criteria prevent persons from participating. These criteria most often include age, gender, the type and stage of an illness, previous treatment history and other medical conditions. All of these criteria are not meant to exclude people personally. They identify the most appropriate people who are needed for the study (such as healthy people versus people with an illness the study intervention intends to treat).