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HIV is a virus that damages white blood cells - Edexcel - GCSE Biology - Question 5 - 2017 - Paper 1
Question 5
HIV is a virus that damages white blood cells. Immunisation could protect people from infection with HIV. In a clinical trial, 16,000 healthy volunteers at risk of... show full transcript
Worked Solution & Example Answer:HIV is a virus that damages white blood cells - Edexcel - GCSE Biology - Question 5 - 2017 - Paper 1
Step 1
Suggest why a placebo injection was used as part of the trial.
Answer
A placebo injection was used as a control to compare the results of the immunisation group against. This helps in determining whether the immunisation itself has any effect, as it allows researchers to see if changes in HIV infection rates are due to the immunisation or other factors.
Step 2
Calculate how many more volunteers contracted HIV after being injected with the placebo compared with those volunteers who were immunised.
Answer
To find the number of volunteers who contracted HIV:
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Calculate the number of volunteers in each group:
- Total volunteers = 16,000
- Volunteers receiving immunisation = 8000 (half of 16,000)
- Volunteers receiving placebo = 8000
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Calculate the number of contracted HIV cases:
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For immunised:
[ 8000 \times 0.00625 = 50 ]
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For placebo:
[ 8000 \times 0.00925 = 74 ]
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Find the difference in the number of cases:
- Difference = 74 - 50 = 24
Thus, 24 more volunteers contracted HIV after being injected with the placebo compared to the immunised group.