Final answer:
A double-blind experiment is when neither the researcher nor the research participants know who has received the treatment.
Step-by-step explanation:
If neither the researcher nor the research participants knows who has received the treatment, the experiment is said to be double-blind. In a double-blind experiment, both the researchers and the participants are blinded, meaning they do not know who is receiving the active treatment and who is receiving the placebo treatment. This helps to eliminate bias and ensure accurate results.
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