Epidemiology: factorial trial design: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Epidemiology: factorial trial design

Sample item

A trial randomises 2,000 children to zinc alone, vitamin A alone, both supplements, or neither, to test the effect of both supplements in one study. Which design is this?

A2 by 2 factorial designBCrossover designCThree-arm parallel designDStepped wedge design

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. 2 by 2 factorial design

A factorial design randomises participants to combinations of two or more interventions so that each can be evaluated, along with their interaction, in a single trial. It is efficient because the same participants answer two questions. A crossover gives every participant each treatment in sequence.

Option by option

A. 2 by 2 factorial design (correct)
Correct. Four combinations allow evaluation of both interventions and their interaction.
B. Crossover design
A crossover design gives treatments in sequence to the same person.
C. Three-arm parallel design
A three-arm parallel design has three groups and no combined arm.
D. Stepped wedge design
A stepped wedge design introduces an intervention to clusters at staggered times.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is A, 2 by 2 factorial design. A factorial design randomises participants to combinations of two or more interventions so that each can be evaluated, along with their interaction, in a single trial.

Why is "Crossover design" not the answer?

A crossover design gives treatments in sequence to the same person.

Why is "Three-arm parallel design" not the answer?

A three-arm parallel design has three groups and no combined arm.

Why is "Stepped wedge design" not the answer?

A stepped wedge design introduces an intervention to clusters at staggered times.

What concept does this question test?

It tests Epidemiology: factorial trial design in PSM. It is efficient because the same participants answer two questions. A crossover gives every participant each treatment in sequence.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Epidemiology: factorial trial design?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.