Sampling methods critique

A question is this type if and only if it asks to identify problems with proposed sampling methods, explain why they are biased, or suggest appropriate sampling methods.

2 questions · Moderate -1.0

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OCR S2 2009 June Q4
7 marks Moderate -0.8
4 A survey is to be carried out to draw conclusions about the proportion \(p\) of residents of a town who support the building of a new supermarket. It is proposed to carry out the survey by interviewing a large number of people in the high street of the town, which attracts a large number of tourists.
  1. Give two different reasons why this proposed method is inappropriate.
  2. Suggest a good method of carrying out the survey.
  3. State two statistical properties of your survey method that would enable reliable conclusions about \(p\) to be drawn.
OCR S2 2010 January Q2
3 marks Easy -1.2
A college has 400 students. A journalist wants to carry out a survey about food preferences and she obtains a sample of 30 pupils from the college by the following method. • Obtain a list of all the students. • Number the students, with numbers running sequentially from 0 to 399. • Select 30 random integers in the range 000 to 999 inclusive. If a random integer is in the range 0 to 399, then the student with that number is selected. If the number is greater than 399, then 400 is subtracted from the number (if necessary more than once) until an answer in the range 0 to 399 is selected, and the student with that number is selected.
  1. Explain why this method is unsatisfactory. [2]
  2. Explain how it could be improved. [1]