A study compares contraceptive methods P and Q. Method P was used by 100 people for one month. Method Q was used by 100 people for one year. Two pregnancies occurred in each group.
A student concludes that the methods are equally effective. Which statement identifies the main problem?
The group sizes match, so the pregnancy counts prove equal effectiveness.
The periods differ, so the pregnancy counts cannot be compared directly.
The group sizes match, so the shorter study must show lower effectiveness.
The periods differ, so the longer study must show greater effectiveness.
48 exam-style questions on Edexcel GCSE Biology 7.2 Reproductive hormones, covering 7.2.1 Stages of the menstrual cycle, 7.2.2 Hormonal control of the menstrual cycle, 7.2.3 Hormonal contraception, 7.2.4 Evaluating contraception methods, and 7.2.5 Hormones in Assisted Reproductive Technology. Each one has a worked solution and a mark scheme showing where the marks go.