Glossary of Clinical Research - R


  • Randomization
  • A method based on chance by which study participants are assigned to a treatment group. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms. The researchers do not know which treatment is better. From what is known at the time, any one of the treatments chosen could be of benefit to the participant (NLM)
  • When referring to an experiment or clinical trial, the process by which animal or human subjects are assigned by chance to separate groups that compare different treatments or other interventions. Randomization gives each participant an equal chance of being assigned to any of the groups. (NCI)
  • The process of assigning trial subjects to treatment or control groups using an element of chance to determine the assignments in order to reduce bias. (ICH E6)
  • Randomized clinical trial
  • A study in which the participants are assigned by chance to separate groups that compare different treatments; neither the researchers nor the participants can choose which group. Using chance to assign people to groups means that the groups will be similar and that the treatments they receive can be compared objectively. At the time of the trial, it is not known which treatment is best. It is the patient's choice to be in a randomized trial. (NCI)
  • A study in which participants are randomly (i.e., by chance) assigned to one of two or more treatment arms of a clinical trial. Occasionally placebos are utilized. (NLM)
  • Recruiting
The period during which a trial is attempting to identify and enroll participants. Recruitment activities can include advertising and other ways of soliciting interest from possible participants (NLM)
  • Recruitment status
Indicates the current stage of a trial, whether it is planned, ongoing, or completed. (NLM)
  • Regimen
A treatment plan that specifies the dosage, the schedule, and the duration of treatment. (NCI)
  • Regulatory Authorities
Bodies having the power to regulate. In the ICH GCP guidance, the expression "Regulatory Authorities" includes the authorities that review submitted clinical data and those that conduct inspections. These bodies are sometimes referred to as competent authorities. (ICH E6)
  • Retrospective
Looking back at events that have already taken place. (NCI)
  • Retrospective cohort study
A research study in which the medical records of groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke and those who do not smoke) are compared for a particular outcome. Also called a historic cohort study. (NCI)
  • Retrospective study
A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called a case-control study. (NCI)
  • Risk-benefit ratio
The risk to individual participants versus the potential benefits. The risk/benefit ratio may differ depending on the condition being treated. (NLM)

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