What is a double-blind study?

A double-blind study is an experimental design where neither the participants nor the researchers know who receives a treatment. This methodology is essential in research, especially in clinical trials, to minimize bias and ensure the validity of the results.

By keeping both the participants and the researchers unaware of who has received the treatment and who has received a placebo (or an alternative treatment), the study can more accurately assess the effectiveness of the intervention. This approach helps to eliminate any influence that expectations or perceptions may have on the outcomes, providing a clearer understanding of the treatment's true effects.

The other options describe scenarios that do not properly capture the essence of a double-blind study. In option B, for instance, if the participants know their treatment but the researchers do not, it still risks bias from the participants' knowledge on the study's outcomes. Option C describes an observational study, which does not involve a treatment or control group, and therefore does not apply to the concept of blinding in trials. Lastly, option D negates the foundational principle of a double-blind study, as awareness of treatment distribution by all parties can lead to planned or unplanned biases that may skew the results.