Sunil takes an extract of 500 cars from the AQA Large Data Set. He wants to estimate the mean CO emission and to compare petrol cars with diesel cars. Some of the diesel cars in his extract have no recorded CO emission.
Sunil deletes every record with a missing CO emission. Explain why his estimate of the mean CO emission may still be biased.
Using your knowledge of the Large Data Set, give one reason why Sunil's estimate does not describe the cars registered in England.
State a diagram Sunil could use to compare the CO emission distributions of the petrol cars and the diesel cars in his extract, and give a reason for your choice.
244 exam-style questions on AQA A Level Maths 2.2 L: Data presentation and interpretation, covering 2.2.1 Single-variable data diagrams, 2.2.2 Scatter diagrams and correlation, 2.2.3 Central tendency, variation and standard deviation, 2.2.4 Outliers and cleaning data, and 2.2 L: Data presentation and interpretation. Each one has a worked solution and a mark scheme showing where the marks go.