Sampling Strategies

Posted by: | Posted on: September 20, 2008

Key Points:

  • Probability sampling is a mechanism for reducing bias in the selection of samples.
  • Ensure you become familiar with key technical terms in the literature on sampling such as: representative sample; random sample; non-response; population; sampling error; etc.
  • Randomly selected samples are important because they permit generalizations to the population and because they have certain known qualities.
  • Sampling error decreases as sample size increases.
  • Quota samples can provide reasonable alternatives to random samples; but they suffer from some deficiencies.
  • Convenience samples may provide interesting data, but it is crucial to be aware of their limitations in terms of generalizability.
  • Sampling and sampling-related error are just two sources of error in social survey research.

Questions for Review

  • What do each of the following terms mean: population; probability sampling; non-probability sampling; sampling frame; representative sample; and sampling and non-sampling error?
  • What are the goals of sampling?

– Sampling error

  • What is the significance of sampling error for achieving a representative sample?

– Types of probability sample

  • What is probability sampling and why is it important?
  • What are the main types of probability sample?
  • How far does a stratified random sample offer greater precision than a simple random or systematic sample?
  • If you were conduciting an interview survey of around 500 people in Manchester, what type of probability sample would you choose and why?
  • A research positions herself on a street corner and asks 1 person in 5 who walks by to be interviewed: She continues doing this until she has a sample of 250. How likely is she to achieve a representative sample?

– The qualities of a probability sample

  • A researcher is interested in levels of job satisfaction among manual workers in a firm that is undergoing change. The firm has 1,200 manual workers. He measures job satisfaction on a likert scale comprising ten items. A high level of satisfaction is scored 5 and a low level is scored 1. The mean job satisfaction score is 34.3. The standard error of the mean is 8.57. What is the 95 per cent condidence interval?

– Sample size

  • What factors would you take into account in deciding how large your sample should be when devising a probability sample?
  • What is non-response and why is it important to the question of whether you will end up whit a representative sample?

– Types of non-probability sample

  • Are non-probability samples useless?
  • In what circumstances might you employ snowball sampling?
  • ‘Quota samples are not true random samples, but in terms of generating a representative sample there is little difference between them, and this accounts for their widespread use in market research and opinion polling.’ Discuss.

– Limits to generalization

  • ‘The problem of generalization to a population is not just to do with the matter of getting a representative sample.’ Discuss.

– Error in survey research

  • ‘Non-sampling error, as its name implies, is concerned with sources of error that are not part of the sampling process.’ Discuss.

Please, use the reference referrin to the source: Alan Bryman. 2004. P.81-82, Second Edition, Oxford University Press