A county contains 60 primary schools and 15 secondary schools. A researcher needs a sample of pupils but has no county-wide list of individual pupils.
Describe a cluster sample that the researcher could take.
Explain one practical advantage of this method.
Explain two ways in which the selected sample could be unrepresentative.
36 exam-style questions on OCR A Level Maths 2.1 Statistical Sampling, covering 2.1.1 Population and sample, 2.1.2 Informal inferences from samples, 2.1.3 Sampling techniques, 2.1.4 Selecting or critiquing sampling techniques, and 2.1 Statistical Sampling. Each one has a worked solution and a mark scheme showing where the marks go.