A physical entity which is the primary unit of operational and/or administrative interest in a study. A physical entity which is the primary unit of operational and/or administrative interest in a study. If the element is present, it must have either a @value, an @id, or extensions Identifiers assigned to this research subject for a study. The current state of the subject. The dates the subject began and ended their participation in the study. Reference to the study the subject is participating in. The record of the person or animal who is involved in the study. The name of the arm in the study the subject is expected to follow as part of this study. The name of the arm in the study the subject actually followed as part of this study. A record of the patient's informed agreement to participate in the study. Candidate Eligible Follow-up Ineligible Not Registered Off-study On-study On-study-intervention On-study-observation Pending on-study Potential Candidate Screening Withdrawn Indicates the progression of a study subject through a study. If the element is present, it must have either a @value, an @id, or extensions