Blind Trial
In a blind (or single-blind) trial, participants do not know which group they're in or what treatment they're receiving. In a double-blind trial, neither participants nor experimenters know group assignments. Blinding prevents both placebo effects and experimenter bias from influencing results.
Real World
During AstraZeneca's clinical trials, neither the nurses administering injections nor the volunteers knew whether they received the real vaccine or saline solution, eliminating both placebo effects and observer bias.
Exam Focus
Name who is 'blind' in single-blind versus double-blind; the mark scheme requires you to identify both parties in double-blind.
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