## **Core Concept**
Randomization in clinical trials is a crucial methodological process used to minimize bias and ensure that the groups being compared are similar in terms of both observed and unobserved factors. This process helps in establishing causality between the intervention and the outcome. By randomly assigning participants to treatment groups, researchers aim to create comparable groups.

## **Why the Correct Answer is Right**
The main purpose of randomization is to ensure that the groups being compared are similar in all aspects, both known and unknown, except for the intervention being tested. This similarity helps in isolating the effect of the intervention on the outcome, thereby reducing confounding variables. Randomization ensures that any differences in outcomes between groups can be attributed to the treatment rather than to pre-existing differences between the groups.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While minimizing bias is indeed a goal of randomization, stating it as ensuring that "bias is completely eliminated" might be too absolute, as randomization primarily aims to distribute both known and unknown factors evenly across groups, not necessarily eliminate bias entirely.
- **Option B:** Although balancing groups in terms of covariates is a result of randomization, saying the main purpose is to "balance covariates" might underrepresent the broader goal of ensuring comparability.
- **Option C:** This option correctly identifies that the main purpose of randomization is to ensure groups are comparable, which directly relates to minimizing confounding variables and ensuring the validity of the causal inference.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that randomization does not guarantee that groups will be identical in all aspects but rather that they will be similar on average. This concept is crucial for understanding the validity and interpretation of clinical trial results.

## **Correct Answer:** C.