Which procedure ensures both the researcher and participants are unaware of group allocations?

The double-blind procedure is the correct answer because it involves both the participants and the researchers being unaware of which group the participants have been assigned to, whether it be the experimental group or the control group. This approach minimizes biases that could affect the outcome of the study.

For instance, if the researcher knows which participants are receiving the treatment and which are not, their expectations could unconsciously influence their behavior towards the participants or how they record data. Similarly, if participants know whether they are receiving the actual treatment or a placebo, their expectations can influence their responses, potentially skewing the results. By keeping both parties blind to the group allocations, the integrity of the data collected is enhanced, leading to more reliable conclusions.

In contrast, a single-blind procedure only keeps the participants unaware of their group assignments, while the researchers are aware of them. The placebo-controlled procedure refers specifically to a study design where participants receive a placebo treatment to compare its effects against a true treatment, but it does not necessarily incorporate the aspect of blinding for both parties. A randomized control trial is a study design that randomly assigns participants to different groups, but it does not inherently ensure that both the researcher and participants are blind to group allocation. Thus, the double-blind