AP Psychology Practice Test 2025 – 400 Free Practice Questions to Pass the Exam

A double-blind procedure is a research design in which neither the participants nor the researchers know who is receiving the treatment and who is receiving a placebo. This method is highly effective in minimizing bias, which is crucial for the integrity of the study. Since both groups are unaware of the treatment allocations, personal expectations and preconceived notions about the treatment's effectiveness do not influence the outcomes. This helps ensure that any changes in the participants' responses can be attributed more reliably to the treatment itself rather than to the influence of the researchers or the participants’ beliefs.

The other options do not accurately capture the main purpose of the double-blind procedure. Ensuring all participants receive the treatment pertains more to study design rather than to blinding. Keeping participants aware of their treatment directly contradicts the idea of a double-blind arrangement. Observing the placebo effect can be part of the outcomes studied, but double-blinding is primarily aimed at reducing bias rather than accentuating the placebo effect specifically.