The OCR Large Data Set records, for each local authority, the number of people in employment and the number who usually travel to work by train.
A student finds positive correlation between these two raw counts. Explain why this does not show that a larger employed population causes people to choose the train, and state how the train variable should be adjusted before comparing local authorities of different sizes.
121 exam-style questions on OCR A Level Maths 2.2 Data Presentation and Interpretation, covering 2.2.1 Tables and diagrams for single variable data, 2.2.2 Area in a histogram, 2.2.3 Scatter diagrams and regression lines, 2.2.4 Informal interpretation of correlation, 2.2.5 Correlation and causation, 2.2.6 Measures of average and spread, 2.2.7 Calculations of mean and standard deviation, 2.2.8 Outliers, 2.2.9 Selecting or critiquing data presentation, and 2.2.10 Cleaning data. Each one has a worked solution and a mark scheme showing where the marks go.