- 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