A data set contains two clusters corresponding to petrol and electric cars. Within each group, mass and energy use have a positive linear association, but the combined data have a negative correlation.
Explain how the grouping variable can produce this reversal.
Explain why one regression line fitted to all cars may be misleading.
State a more appropriate analysis.
105 exam-style questions on WJEC A Level Maths 2.2 Data presentation and interpretation, covering 2.2.1 Data presentation and interpretation, 2.2.2 Data presentation and interpretation, 2.2.3 Data presentation and interpretation, 2.2.4 Data presentation and interpretation, 2.2.5 Data presentation and interpretation, 2.2.6 Data presentation and interpretation, 2.2.7 Data presentation and interpretation, 2.2.8 Data presentation and interpretation, and 2.2 Data presentation and interpretation. Each one has a worked solution and a mark scheme showing where the marks go.