Final answer:
A double-blind research study is one where neither researchers nor participants know who is in the control or experimental group, thus preventing experimenter bias and the placebo effect.
Step-by-step explanation:
A double-blind research study is one in which neither the researchers nor the participants know the predicted outcome or who has been placed in the control or experimental group. This form of study design is crucial for eliminating biases such as the experimenter bias and placebo effect. Experimenter bias can occur when a researcher's expectations inadvertently influence the results of the study.
To avoid this, in double-blind studies, those who score the tests or collect data are unaware of each participant's group assignment. Meanwhile, the placebo effect reflects the impact of a participant's expectations on the study's outcomes. By not knowing whether they are receiving a real treatment or a placebo, participants' responses are less likely to be influenced by their expectations, contributing to more reliable and valid results.