How are new vaccines and drugs tested to be sure they are safe and effective?
The design of clinical trials of vaccines and drugs, including randomisation, the use of placebo and control groups, double-blind protocols, the importance of a large enough sample size for statistical significance, and the phases of testing.
An SQA Higher Human Biology answer on clinical trials of vaccines and drugs, covering randomisation, placebo and control groups, double-blind protocols, the need for a large enough sample for statistical significance, and the phases of clinical testing before a treatment is approved.
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What this dot point is asking
The SQA wants you to explain how clinical trials of vaccines and drugs are designed, including the use of randomisation, placebo and control groups and double-blind protocols, explain why a large enough sample size is needed for statistical significance, and describe the phases of testing.
Control groups and placebos
A trial compares a group given the new treatment with a control group:
Without a placebo control, it would be impossible to tell whether the treatment really worked.
Randomisation and double-blind protocols
Two further features remove bias from the trial:
- Randomisation. Subjects are allocated to the treatment or placebo group at random. This removes selection bias and makes the two groups as similar as possible, so any difference in outcome is due to the treatment rather than to differences between the groups.
- Double-blind protocol. Neither the subjects nor the researchers know who is receiving the real treatment until the trial ends. This prevents the subjects' expectations and the researchers' judgements from biasing how effects are reported and assessed.
Sample size and statistical significance
A trial must use a large enough sample of subjects so that the result is reliable and any difference seen is not simply due to chance or to natural variation between individuals. A larger sample makes it easier to detect a genuine effect and gives greater confidence in the conclusion. New treatments are tested in phases, beginning with small groups to check safety and then moving to larger groups to test effectiveness, before approval.
Examples in context
Example 1. Testing a new vaccine. A new vaccine is given to a large randomised group while a control group receives a placebo, in a double-blind design. Only if significantly fewer people in the vaccinated group catch the disease is the vaccine judged effective, showing why controls and randomisation matter.
Example 2. Why early results can mislead. A drug that looks promising in a tiny early trial may show no real benefit when tested in thousands of people. This is why trials progress through phases with increasing sample sizes before a treatment is approved.
Try this
Q1. State what a placebo is in a clinical trial. [1 mark]
- Cue. A dummy treatment with no active drug, given to the control group for comparison.
Q2. Explain why a double-blind protocol reduces bias in a clinical trial. [1 mark]
- Cue. Neither the subjects nor the researchers know who is receiving the real treatment, so expectations cannot influence how effects are reported or assessed.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher 20194 marksExplain why a clinical trial of a new drug uses a placebo, randomisation and a double-blind protocol.Show worked answer →
A 4-mark answer needs the purpose of each feature.
A placebo is a dummy treatment with no active drug, given to a control group. Comparing the drug group with the placebo group shows whether any effect is due to the drug itself rather than to the act of being treated (the placebo effect).
Randomisation means subjects are allocated to the drug or placebo group at random. This removes bias and ensures the two groups are as similar as possible, so any difference in outcome is due to the treatment rather than to differences between the groups.
In a double-blind protocol, neither the subjects nor the researchers know who is receiving the drug or the placebo until the end. This prevents bias in how subjects report effects and how researchers assess them.
Award (1) placebo as a control to show the effect is due to the drug, (2) randomisation removes bias and balances the groups, (3) double-blind means neither subject nor researcher knows the allocation, and (4) this prevents bias in reporting and assessment.
SQA Higher 20213 marksExplain why a clinical trial must use a large enough sample size, and what is meant by a result being statistically significant.Show worked answer →
This is a 3-mark question on sample size and significance.
A clinical trial must use a large enough group of subjects so that the results are reliable and any difference seen between the treatment and control groups is not simply due to chance or to natural variation between individuals.
A result is statistically significant when the difference between the groups is large enough that it is very unlikely to have happened by chance, so it can be concluded that the treatment really did have an effect. A larger sample makes it easier to detect a genuine effect and to be confident in the result.
Award (1) a large sample makes the result reliable and reduces the effect of chance and individual variation, (2) statistically significant means the difference is unlikely to be due to chance, and (3) a larger sample gives greater confidence in detecting a real effect.
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