Terms starting with R

Random Allocation

Random allocation is when clinical study participants are assigned to different treatment groups by chance.


Randomization is the process by which two or more alternative treatments are assigned to volunteers by chance rather than by choice. (NIH)

Randomization Number

A randomization number is a unique number assigned to each randomized participant in a clinical study that corresponds to a specific treatment group assignment. It is used to identify individuals, but still maintains anonymity.

Randomized Allocation

Randomized allocation is when clinical study participants are assigned to different treatment groups by chance.

Raw Data

Raw data is the data that was originally collected during the course of a clinical study but has not been processed in any way and does not include conclusions or interpretations. Raw data includes: records of original observations, measurements, and activities (such as laboratory notes, evaluations, data recorded by automated instruments); and researcher's records of participants, such as participant medical charts, hospital records, X-rays, and attending physician's notes. (CDISC)


Recruitment is the process investigators use to find and enroll appropriate clinical study participants (using the protocol's inclusion and exclusion criteria).

Recruitment Period

The recruitment period is the length of time during which investigators enroll participants into a clinical study.

Recruitment Plan

The recruitment plan outlines how individuals will be recruited for a clinical study and how the clinical study will reach the recruitment goal. (NIH)

Recruitment Status

The recruitment status indicates the progress of a clinical study in regards to recruiting participants. Specific terms that indicate recruitment status include: Not yet recruiting: the clinical study has not started recruiting participants; Recruiting: the clinical study is currently recruiting participants; Enrolling by invitation: the clinical study is only selecting its participants from a specific patient population, or group of people, decided on by the researchers in advance; Active, not recruiting: the clinical study is ongoing, and participants are receiving an intervention or being examined, but new participants are not currently being recruited or enrolled; Suspended: the clinical study has stopped early but may start again; Terminated: the clinical study has stopped early and will not start again; Completed: the clinical study has ended normally, and participants are no longer being examined or treated; Withdrawn: the clinical study stopped early, before enrolling its first participant; Unknown: the clinical study has passed its completion date, but the recruiting status has not been verified within the past two years.

Recruitment Target

The recruitment target is the number of participants that must be recruited as candidates for enrollment into a clinical study to meet the requirements of the protocol. In multicenter studies, each investigator has a recruitment target. (CDISC)

Refuse to Participate

"Refuse to participate" is when a person (for any reason) voluntarily decides they would not like to participate in a clinical study."


Registration is the process of submitting and updating summary information about a clinical study and its protocol, from its beginning to end. This needs to be a structured, public Web-based study registry that is accessible to the public, such as ClinicalTrials.gov. (CTG)


Reimbursement refers to when those in charge of conducting a clinical study provide some form of compensation to participants. This may take the form of money, or the reimbursement of travel expenses, food, food vouchers, or other services.

Remote Clinical Trial

A remote clinical trial utilizes some form(s) of virtual contact with participants (e.g., via electronic communication, etc.) to reduce or eliminate the need for participants to travel to an investigative site for treatment and other clinical study related procedures.


Replacement is the act of enrolling a clinical study participant to compensate for the withdrawal of another. (CDISC)

Reporting Group

Investigator sometimes organize participants into reporting groups to better summarize the information collected during the study. This grouping may be the same as or different from the study groups. (CTG)

Rescue Medications

Rescue medications are medical products listed in the clinical study protocol that can be given to clinical study participants when the effect of the clinical study treatment is not satisfactory, is too strong and likely to cause a hazard to the participant, or if there is any other emergency situation.

Research Hypothesis

A research hypothesis is what the investigators set out to support (or disprove) by performing the clinical study.

Responsible Party

The responsible party is the person whose job it is to submit information about a clinical study to ClinicalTrials.gov and also regularly update that information. This is usually the clinical study sponsor or investigator. (CTG)

Results Database

A results database is a structured online system, such as the ClinicalTrials.gov results database, that provides the public with access to registration and summary results information for completed or terminated clinical studies. (CTG)

Results Delayed

"Results delayed" indicates that the sponsor or investigator submitted an extension request because they need more time to publish the results of their clinical study. (CTG)

Results First Submitted that Met quality control (QC) Criteria

"Results first submitted that met quality control (QC) criteria" is the date when the study sponsor or investigator first submits results that meet the National Library of Medicine (NLM) QC review criteria. The sponsor or investigator may need to revise and submit results information one or more times before NLM's QC review criteria are met. (CTG)"

Retention Plan

The retention plan details how the clinical study will keep participants enrolled. (NIH)

Retrospective Study

A retrospective study collects information on events that occurred before the clinical study starts (i.e., backward-looking).


In clinical studies, risk is the probability a participant will experience harm or discomfort. Risk is stratified in various scales (e.g., minimal risk, low risk, medium risk and high risk).

Route of Administration

The route of administration is the path by which a medicine is taken into or makes contact with the body (for example orally or via a patch).

Run-in Period

The run-in period is the length of time before a clinical study starts when the investigators do not give the participants the medicine that is being tested. During this time participants may still receive standard treatments for their disease. as long as these treatments are allowed in the clinical study's design.