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GCSE Biology · key term
A systematic influence that could make a comparison unfair or distort its results.
Used by AQA, Edexcel and OCR
Specification 4.2.2.6 · Paper 1
A consistent distortion in results caused by the way a study or sample is designed, selected, measured or reported.
Revise: The Impact and Epidemiology of Non-Communicable DiseaseA voluntary survey can also produce volunteer bias if people with strong views or particular experiences are more likely to respond. Non-response can introduce further bias if those who reply differ from those who do not.
Specification 5.20 · Paper 1
Explain why controls are used: a placebo provides a comparison, while blinding reduces bias. Do not claim that the placebo contains the active medicine.
When explaining double-blind trials, state who is unaware of the treatment allocation and connect this explicitly to reducing bias.
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A systematic influence on decisions, observations or reported results that can make a comparison unfair.
In a double-blind trial, neither the participants nor the clinicians assessing them know who received the active medicine and who received the placebo while results are being collected. This reduces bias: participants' expectations are less likely to change what they report, and clinicians' expectations are less likely to affect how they assess the outcomes.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A systematic effect that makes a sample or measurement unrepresentative and may distort the conclusion.
Revise: Data AnalysisIf a study of a disease affecting all adults recruited only young gym users, its findings might not apply to older adults or less active people. This is sampling bias: the selection method systematically favours some members of the population over others.