Health workers in two districts followed equal-sized groups of pregnant patients diagnosed with HIV. Each group contained 400 patients and was followed over the same period.
Some patients received antiretroviral drugs during pregnancy and birth. The babies were later tested for HIV.
| District | Number of patients receiving antiretroviral drugs | Number of babies diagnosed with HIV |
|---|---|---|
| P | 240 | 36 |
| Q | 360 | 12 |
Calculate the percentage reduction in the number of babies diagnosed with HIV from district P to district Q.
Explain how antiretroviral drugs could have produced the pattern in the table.
Explain one limitation of using these results to conclude that the difference in treatment caused the difference in the number of babies diagnosed with HIV.
112 exam-style questions on Edexcel GCSE Biology 5.1 Health and communicable disease, covering 5.1.1 Communicable and non-communicable diseases, 5.1.2 Disease susceptibility interactions, 5.1.3 Pathogens as disease-causing organisms, 5.1.4 Common infections, 5.1.5 Spread and prevention of pathogens, 5.1.6 Lifecycle of a virus, and 5.1.7 Spread and prevention of STIs. Each one has a worked solution and a mark scheme showing where the marks go.