For a sample of 200 cars there is positive correlation between a car's age, in years, and its CO emission. A student concludes that a car's engine produces more CO as the car gets older.
Suggest a third factor that could be responsible for the correlation.
Explain how that factor could produce the correlation even if a car's age had no effect at all on its CO emission.
Describe how the student could investigate the effect of age alone.
157 exam-style questions on AQA A Level Maths 2.2.2 Scatter diagrams and correlation. Each one has a worked solution and a mark scheme showing where the marks go.