GCSE · Sampling
Bias & sampling methodsExam-style questions
What bias really is — a method that systematically leaves people out, so a bigger sample never fixes it — how to name who is missing, the strengths and weaknesses of random, systematic, stratified and convenience sampling, and how to criticise and rewrite a questionnaire.
11 questions · GCSE (Higher) level · mark scheme and worked solution on each · no sign-up to try
- 1A charity wants to estimate the mean number of hours per week that adults in a city spend doing voluntary work. The charity emails a questionnaire to the 4000 adults on its mailing list. 300 of them reply.
(a) Explain why the mean found from these 300 replies is likely to be too high. Your answer must say who is over-represented and who is left out.
(b) A trustee suggests emailing all 4000 people on the list a second time, to collect more replies. Explain whether this would remove the problem described in part (a).
(c) Describe a sampling method that would give the charity a more reliable estimate. You must say how the people in the sample would be chosen.Level 5 · 5 marksTry it - 2A company has 500 employees. Its staff list is arranged in departments. Every department contains exactly 10 employees, and within each department the manager is listed first, followed by the 9 other employees of that department.
A researcher takes a systematic sample of 50 employees: she picks one of the first 10 names at random, then takes every 10th name after it.
(a) Explain why her sample may be very unrepresentative, even though her starting name was chosen at random.
(b) The researcher repeats her method on a longer staff list of 1000 employees, arranged in exactly the same way, to get a sample of 100. Explain why this does not fix the problem.
(c) Describe how she could instead choose a sample of 50 that represents managers and other employees fairly.Level 5 · 5 marksTry it