## Core Concept
A double-blind study is a research design used in clinical trials where both the participants and the researchers are unaware of certain critical aspects of the study, typically the treatment assignments. This method helps reduce bias and enhances the reliability of the results.

## Why the Correct Answer is Right
In a double-blind study, participants and researchers are both blinded to the treatment assignments. This means that neither the participants nor the researchers know who is receiving the active treatment and who is receiving the placebo or control treatment. This design helps minimize bias from both sides, increasing the validity of the study findings.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not provided, but typically, incorrect options might state that a double-blind study involves only participants being unaware or only researchers being unaware, which does not accurately describe the double-blind design.
- **Option B:** Similarly, this option is not provided, but it might inaccurately describe the study design, such as suggesting that only one group is blinded or that the study is open-label.
- **Option C:** Without the specific details of option C, it's hard to address directly, but any option that does not accurately reflect the mutual blinding of participants and researchers would be incorrect.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the purpose of a double-blind study is to reduce bias. By keeping both participants and researchers unaware of treatment assignments, the study aims to provide more objective results. This is particularly important in clinical trials evaluating the efficacy of new drugs or treatments.

## Correct Answer: D.