In a clinical study, participants are often divided into groups.
In interventional studies, participants are assigned
to receive one or more interventions (or no intervention)
so that researchers can evaluate the effects of the interventions on
biomedical or health-related outcomes.
Arm refers to each group or subgroup of participants in a clinical trial that receives specfic
interventions (or no intervention) according to the study protocol.
This is decided before the trial begins.
In observational studies, participants may receive
diagnostic, therapeutic, or other types of interventions,
but the investigator does not assign participants to specific interventions (as in an interventonal study.)
Group or cohort refers to participants that are identified as belonging to a study group
that is assessed for biomedical or health outcomes.