Parallel Group — What It Means in Clinical Trials
Plain English Definition
In a parallel-group trial, participants are split into separate groups and each group receives a different treatment for the entire study. Unlike a crossover trial, you stay in your assigned group from start to finish and do not switch treatments.
Why It Matters
Most large clinical trials use a parallel-group design. Understanding this means knowing that your treatment assignment is fixed — you will not switch to a different group partway through.
Example
A listing might state: "Parallel-group study with three arms: Drug X low dose, Drug X high dose, and placebo." Each participant stays in one group for the whole study.
Need help understanding eligibility criteria?
How to Read Eligibility Criteria →