In a double-blind randomized controlled trial, 'blinding' refers to masking allocation from:
- A Only the participants, to prevent outcome reporting bias
- B Both participants and investigators/assessors, to prevent performance and detection bias ✓
- C Only the statistician analyzing the data
- D The ethics committee reviewing the trial protocol
Correct answer: B. Both participants and investigators/assessors, to prevent performance and detection bias
Explanation
In a double-blind trial, both the participant (preventing reporting/compliance bias) and the investigator/healthcare provider (preventing performance bias and detection bias) are masked to treatment allocation. Triple-blinding additionally masks the data analyst. Blinding is critical for subjective outcomes; it is impossible for surgical trials. Allocation concealment (different from blinding) prevents selection bias before randomization.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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