Question

In a controlled trial to compare two treatments, the main purpose of randomization is to ensure that:

• A. The two groups will be similar in prognostic factors.
• B. The clinician does not know which treatment the subjects will receive.
• C. The sample may be referred to a known population.
• D. The clinician can predict in advance which treatment the subjects will receive.

Hint:

Randomization balances known and unknown prognostic factors between groups; blinding, not randomization, hides the treatment assignment.

Answer 1

The Correct Option is A

Step 1: Understanding the Question.
We are asked why randomization is used when assigning patients to two treatment groups in a controlled trial.

Step 2: Key Concept.
Randomization means each patient has an equal, chance-based likelihood of being placed in either treatment group, decided by a method like a random number table rather than by the clinician's choice. Its main job is to spread both known and unknown prognostic factors (age, disease severity, other illnesses, and so on) evenly across the two groups by chance, so that at the start of the trial the groups are comparable, and any later difference in outcome can be credited to the treatment rather than to a difference that existed before the trial began.

Step 3: Detailed Explanation.
Option (A) matches this purpose directly: randomization balances prognostic factors between the two groups so the comparison is fair from the outset. This is correct.
Option (B), the clinician not knowing which treatment a subject gets, describes blinding (masking), a separate design feature used to stop bias in assessment or care, not randomization itself.
Option (C), referring the sample to a known population, is really about how the sample was chosen (sampling method) and about external validity, not about how patients are split between treatment arms.
Option (D) describes the opposite of what a well-run trial wants: if the clinician could predict in advance which treatment a subject will get, the assignment is not truly random, and this predictability can itself introduce selection bias.

Step 4: Final Answer.
Randomization is mainly done to make sure the two treatment groups start out similar in prognostic factors, so the trial gives a fair comparison.
\[ \boxed{\text{The two groups will be similar in prognostic factors}} \]