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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 to serve as a control group, allowing for comparison against the vaccinated group. This helps determine the effectiveness of the immunisation by isolating the effects of the vaccine from psychological factors related to receiving a treatment.
Step 2
Calculate how many more volunteers contracted HIV after being injected with the placebo compared with those volunteers who were immunised.
Answer
To determine the number of volunteers who contracted HIV, we first calculate the number of volunteers in each group:
- Total volunteers = 16000
- Volunteers receiving immunisation = 8000 (half of 16000)
- Volunteers receiving placebo = 8000 (the other half)
Next, we calculate the number of HIV cases for each group:
-
Volunteers with HIV after immunisation:
-
Volunteers with HIV after placebo injection:
Now, subtract the two results to find the difference:
Thus, 24 more volunteers contracted HIV after being injected with the placebo compared to those who received the immunisation.