1.9 What is a double-blind experiment?
1.9.1 Research participant bias is a problem in some studies; the placebo effect is a source of research participant bias in experiments involving drugs.
1.9.2 A related problem is researcher bias. Researcher expec-tations can create a self-fulfilling prophecy, in which a participant changes in the direction of the expectation.
1.9.3 In a double-blind experiment, neither the research participants nor the researchers collecting data know who was in the experimental group or the control group, allowing valid conclusions to be drawn.