An article called "The Placebo Effect Works and You Can Catch It From Your Doctor" describes a study to
investigate whether patients can pick up subtle facial cues that reveal their doctor's beliefs about the
effectiveness of a treatment. The article included this study description:

Researchers randomly assigned undergraduate students to play the role of a patient or a doctor.
The "patients" were given a controlled heat stimulus to the forearm, after receiving one of two
types of cream from the "doctor." Students in the doctor group had previously been conditioned to
believe that one of the creams was pain reliever. But in reality both of the two creams that they
administered were an identical petroleum-jelly based placebo. And yet, when the doctor actors
believed that the cream was a real medication … the patient actors reported experiencing
significantly lower amounts of pain.

(a) The article also includes the statement, "Avoiding these placebo effects is one reason for double blind
studies." Explain what the term double-blind means.

Double-blind refers to neither the study participants nor those measuring the response or
providing the treatment knowing what treatment was received.
Double-blind refers to only the study participants not knowing which treatment they received or
what the purpose of the experiment is before it is conducted.
Double-blind refers to only the researchers not knowing which treatment a participant received or
personal information about the participant.
Double-blind refers to researchers using anonymous third parties to measure the response. Only
those measuring the response do not know which treatment was received.