Two surveys estimate support for a transport proposal. Survey A is an open online poll with 5000 responses. Survey B is a stratified random sample of 400 residents, with 68% response within each age stratum.
Explain why the larger response count does not necessarily make Survey A more reliable.
Identify one remaining source of bias in Survey B.
Describe two checks or refinements before using Survey B to infer support among all residents.
36 exam-style questions on OCR (MEI) A Level Maths 2.1 Sampling, covering 2.1.1 Population and sample, 2.1.2 Samples to make informal inferences, 2.1.3 Random sampling, 2.1.4 Variety of sampling techniques, 2.1.5 Select or evaluate sampling techniques, and 2.1 Sampling. Each one has a worked solution and a mark scheme showing where the marks go.