A company wants to test the effectiveness of a new acne cream. The company recruits 500 girls ages 13 to 17 who have acne. The subjects are randomly assigned into two groups. One group is given the acne cream and the other is given a placebo that looks exactly like the acne cream. Both groups apply the cream daily for two months. Facial photos are taken at the beginning and end of the treatment to compare results.
c. How could this experiment be designed to be double-blind?

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Define the concept of a double-blind experiment: In a double-blind experiment, neither the participants nor the researchers interacting with them know which group (treatment or placebo) the participants belong to. This helps eliminate bias from both the participants and the researchers.

Step 1: Ensure that the participants (the 500 girls) do not know whether they are receiving the acne cream or the placebo. This can be achieved by making the placebo look, feel, and smell identical to the actual acne cream.

Step 2: Ensure that the researchers who interact with the participants (e.g., those distributing the creams or taking the facial photos) also do not know which participants are in the treatment group and which are in the placebo group. This can be done by coding the creams with labels (e.g., 'A' and 'B') that do not reveal their contents.

Step 3: Assign a third party (e.g., a statistician or a separate team) to manage the random assignment of participants to the treatment and placebo groups and to keep track of which label corresponds to which group. This information should be kept confidential until the experiment is complete.

Step 4: After the two-month treatment period, collect and analyze the data (e.g., comparing the before-and-after photos) without revealing the group assignments. Only after the analysis is complete should the group assignments be unblinded to interpret the results.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Double-Blind Study

A double-blind study is a research design where neither the participants nor the researchers know who is receiving the treatment or the placebo. This method helps eliminate bias in the results, as it prevents expectations from influencing the participants' responses and the researchers' assessments. In the context of the acne cream experiment, both the girls and the individuals administering the treatment should be unaware of which group receives the actual cream and which receives the placebo.

Random Assignment

Random assignment is a technique used in experiments to ensure that each participant has an equal chance of being placed in any group. This process helps to control for confounding variables and ensures that the groups are comparable at the start of the experiment. In the acne cream study, random assignment of the 500 girls into the treatment and placebo groups is crucial for the validity of the results.

Placebo Effect

The placebo effect occurs when participants experience a perceived improvement in their condition due to their belief in the treatment, rather than the treatment itself. This psychological phenomenon can significantly impact the outcomes of clinical trials. In the acne cream study, using a placebo that looks identical to the actual cream helps to control for the placebo effect, allowing researchers to more accurately assess the true effectiveness of the acne treatment.

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