Question

from 2010 to 2015, a group of researchers conducted an experiment using two types of pain medication: pill a and pill b. the researchers gave the doctors the pills in unidentified packages so they would not know which package was pill a and which package was pill b. the patients participating did not know which pill they received either. what is this an example of?
the effect of a treatment unit
the placebo effect
a control group study
a double - blind study
voluntary response bias

Explanation:

This is a study where neither the researchers/doctors nor the patients know which treatment (pill A or B) is being administered, which fits the definition of a double-blind study. Other options do not match: a control group study requires a non-treated comparison group, the placebo effect refers to a response from an inactive treatment, treatment effect is the impact of a treatment, and voluntary response bias is a sampling issue.

Answer:

A double-blind study