A randomised controlled trial uses allocation concealment but does not blind participants or outcome assessors. Which type of bias is most likely to be introduced?
- A Performance bias and detection bias ✓
- B Selection bias at enrolment
- C Attrition bias from differential dropout
- D Reporting bias from selective publication
Correct answer: A. Performance bias and detection bias
Explanation
Allocation concealment prevents selection bias at the point of randomisation. However, if participants and outcome assessors know the group assignment (absence of blinding), performance bias (participants or caregivers behaving differently) and detection bias (outcome assessors measuring outcomes differently) become threats to internal validity. Attrition bias arises from differential follow-up loss; reporting bias involves selective publication or outcome reporting — neither is primarily introduced by lack of blinding per se.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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