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A trial in which neither the participants nor the clinicians assessing them know who receives the medicine and who receives the placebo until the results have been collected.

A trial in which neither the patients nor the doctors assessing them know who receives the drug and who receives the placebo until the results are collected.

In a double-blind trial, neither the patients nor the doctors assessing them know during the trial who receives the active drug and who receives the placebo. This reduces two possible sources of bias: patients' expectations are less likely to alter how they describe symptoms, and doctors' expectations are less likely to affect how they assess or record outcomes. Treatment identities can be revealed after the results have been collected so that the groups can be compared.

For double-blind trials, state both who is unaware of the treatments and why: neither the patients nor the doctors know who receives the drug, reducing bias.

In a double-blind trial, neither the participants nor the researchers assessing them know who receives the medicine until the results have been collected.

When explaining double-blind trials, state who is unaware of the treatment allocation and connect this explicitly to reducing bias.

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.

A trial in which neither the participants nor the researchers assessing them know who has received the medicine or the comparison treatment until the results have been collected.

In a double-blind trial, neither the participants nor the researchers assessing them know who has received the medicine and who has received the comparison treatment while results are being collected. This reduces the chance that expectations will influence reported symptoms, observations or measurements. The groups can then be revealed and their results compared.

A trial in which neither the participant nor the doctor assessing them knows which treatment they receive during the trial.

In a double-blind trial, neither the participant nor the doctor assessing them knows the allocation while the trial is under way. Double blinding reduces the chance that expectations influence reported symptoms, care or assessment.

Double-blind trial

Definition

How each exam board covers it

AQA GCSE Biology · 8461

Edexcel GCSE Biology · 1BI0

Exam tips

Revise Biology with GradeGen

OCR GCSE Biology A · J247

OCR GCSE Biology B · J257