Double Blind Trial
In a double blind trial, both participants and experimenters are unaware of treatment assignments. This eliminates bias from expectations: placebo effects in participants and experimenter expectations (observer bias) are controlled.
Real World
In GlaxoSmithKline's antidepressant trials, identical-looking sugar pills and real tablets are given coded labels so neither the patient nor the doctor recording symptom scores knows which is which.
Exam Focus
Name both biases eliminated — placebo effect (participant) and observer bias (experimenter) — for full marks.
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