Crossover trial vs Parallel trial
How to tell Crossover trial and Parallel trial apart when a board question makes them look alike.
Crossover trial: each patient receives both treatments in sequence as their own control; parallel trial: each patient stays in one group.
Side by side
Crossover trials have each participant receive both treatments in sequence separated by washout, serving as their own control.
Parallel trials assign participants to one treatment arm for the study duration without switching arms.
Crossover trials have each participant receive both treatments in sequence separated by washout, serving as their own control.
Parallel trials assign participants to one treatment arm for the study duration without switching arms.
Crossover trials require washout periods and are threatened by carryover and period effects.
Parallel trials avoid carryover from switching treatments but need separate groups with balanced baseline risk.
The trap
Crossover uses within-person comparison; parallel keeps separate groups.
The repair move
Before naming the answer, force the stem through the separator: Crossover uses within-person comparison; parallel keeps separate groups.
Try a free question
CoreA clinical trial of a new antihypertensive drug enrolls 200 patients. Each patient receives BOTH the new drug for 8 weeks AND placebo for 8 weeks (with a 2-week washout period between), with the order randomized. Each patient serves as their own control. Which study design is this?
Show answer and explanation
Answer: A. Crossover trial. Crossover trial assigns each participant to receive both treatments in sequence with a washout period between. Within-person comparison reduces inter-individual variability and requires smaller sample size. Appropriate for chronic stable conditions where disease persists between periods (hypertension, asthma, chronic pain). NOT appropriate for acute conditions, curative interventions, or interventions with carryover effects.
Why the other choices are tempting
- B. Parallel trial assigns each participant to one treatment group for the entire study without switching.
- C. Factorial trial tests multiple interventions simultaneously in a factorial design (e.g., 2x2).
- D. Cluster randomized trial randomizes groups (clinics, communities) rather than individuals.
- E. Adaptive trial modifies design based on accumulating data.
Flashcards
Tap a card to flip it.
What clue supports Crossover trial?
Choose Crossover trial when the stem gives this pattern: Crossover trials have each participant receive both treatments in sequence separated by washout, serving as their own control.
What clue supports Parallel trial?
Choose Parallel trial when the stem gives this contrasting pattern: Parallel trials assign participants to one treatment arm for the study duration without switching arms.
Quick answers
What is the fastest way to tell Crossover trial from Parallel trial?
Crossover trial: each patient receives both treatments in sequence as their own control; parallel trial: each patient stays in one group.
What is the key clue for Crossover trial?
Crossover trials have each participant receive both treatments in sequence separated by washout, serving as their own control.
What is the key clue for Parallel trial?
Parallel trials assign participants to one treatment arm for the study duration without switching arms.
What is the common trap with Crossover trial vs Parallel trial?
Crossover uses within-person comparison; parallel keeps separate groups.