Social Research

Fourth edition

by Sotirios Sarantakos

Chapter 7 - Sampling Procedures

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Educational objectives
After completing this chapter, you will:
  1. be able to explain the nature and process of sampling in social research;
  2. understand the main types of sampling and the areas in which they can be applied;
  3. have knowledge of the advantages and disadvantages of sampling in general and of the sampling methods in particular;
  4. be in a position to apply sampling in actual situations;
  5. have a clear understanding of the ways in which sampling procedures are employed in qualitative and quantitative research, and their logical and methodological foundation.

Contents

  1. Reasons for sampling
  2. Principles of sampling
  3. Types of sampling
  4. Probability (random) sampling
  5. Non-probability sampling
  6. Sampling procedures in qualitative research
  7. Internet sampling
  8. Sample size
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Points to remember

The following are the major points introduced in this chapter. Ensure that you are very confident with their meaning, content, context and significance.
  1. Sampling is the process of choosing the respondents and the units of the study in general.
  2. Sampling is a common practice and an indispensable research tool in social sciences.
  3. Sampling, as the alternative to conducting a saturation survey, offers many advantages.
  4. Sampling units must be chosen objectively and systematically, must be easily identifiable and clearly defined, independent from each other, not interchangeable, and free of errors, bias and distortions.
  5. The two distinct types of sampling are probability and non-probability sampling.
  6. In a probability sampling, all units have an equal, calculable and non-zero probability to be included in the sample.
  7. Non-probability sampling does not adhere to the rules of probability.
  8. The two types of probability sampling are simple random sampling and systematic sampling.
  9. In a simple random sampling all units of the target population have an equal chance of being selected.
  10. The three most common techniques of selection used in simple random sampling are the lottery method, the method of random numbers and the computer method.
  11. In systematic sampling although all units have an equal chance of being selected, their selection depends on the choice of other units.
  12. Systematic sampling employs the sampling fraction method of choosing the respondents.
  13. Stratified random sampling is the procedure in which the sample is chosen after the target population is divided in a number of strata, from which the respondents are taken.
  14. Cluster sampling is the procedure in which in the first instance clusters are chosen.
  15. In multi-stage sampling, samples are chosen in stages: firstly one sample is taken and then a second or third sample is chosen from within the previous sample.
  16. In multi-phase sampling the procedure followed is the same as in multi-stage sampling with the difference that in each stage of sampling data is collected.
  17. Area sampling is the procedure in which the choice of respondents is related to geographical areas. An area is divided into smaller sections, progressively leading to smaller samples and ultimately to the respondents.
  18. Panel samples include a number of respondents chosen in a systematic way and subjected to data collection on more than one occasion.
  19. Spatial sampling is a procedure in which a sample is taken from people temporarily congregated in space.
  20. Accidental sampling is a non-probability sampling procedure in which the researcher chooses a number of respondents at will. It is also called convenience sampling, chunk sampling, grab sampling or haphazard sampling.
  21. In purposive sampling the researcher chooses the respondents who are thought to serve the purpose of the study. It is also called judgemental sampling.
  22. Quota sampling is the procedure in which the researcher chooses a quota of respondents set by the project manager
  23. Snowball sampling is a procedure in which the selection of additional respondents is guided by respondents who have already been studied.
  24. In theoretical sampling the choice of respondents is guided by the emerging theory.
  25. Sampling procedures are employed in all quantitative studies but elements of sampling are found also in qualitative research.
  26. Non-response is a serious research problem that investigators must deal with.
  27. Sample size is computed by means of statistical and non-statistical procedures.
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Short-answer questions

  1. Give a brief description of the nature and purpose of sampling in quantitative and qualitative research.
  2. What is a complete coverage study?
  3. What is meant by a 'saturation survey'?
  4. Describe briefly the differences between target population and survey population.
  5. List the main reasons for employing sampling procedures.
  6. In what ways can a study based on sampling offer more detailed information than a saturation study?
  7. Discuss briefly the main principles of sampling.
  8. What are the basic types of sampling? List their main similarities and differences.
  9. What are the most common types of probability sampling?
  10. Describe the method of random numbers in sampling.
  11. How are samples established when using the lottery method of selection?
  12. What are the main features of simple random sampling?
  13. What are the main attributes of systematic sampling?
  14. What are the main differences between systematic sampling and simple random sampling.
  15. Describe briefly the nature and use of 'sampling frames' in social research.
  16. Explain the nature and use of the sampling fraction method.
  17. Describe the nature and types of stratified sampling.
  18. Explain the nature and use of cluster sampling.
  19. Describe briefly the nature and purpose of multi-phase sampling.
  20. What is an area sampling and how useful is it for social research?
  21. Describe the nature and types of longitudinal studies.
  22. What are the main criteria of non-probability sampling?
  23. What are the main types of non-probability sampling?
  24. How is a sample chosen when the method of accidental sampling is used?
  25. What is the nature and purpose of purposive sampling?
  26. Describe briefly the selection of a sample when using the process of quota sampling.
  27. Explain the nature and purpose of snowball sampling.
  28. What are the main differences between quantitative and qualitative sampling procedures?
  29. What are the main types of sampling that are employed in qualitative social research?
  30. Describe briefly the process and purpose of theoretical sampling.
  31. What are the main characteristics of sampling procedures employed by qualitative research?
  32. What is meant by non-response in social research and how is it controlled?
  33. What are the ways of estimating the ideal sample size?
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Practical exercises

  1. You have been asked to investigate the views of nurses working in ten large hospitals to establish their views as to whether health workers, and medical doctors in particular, should be allowed to strike.
    a) What is the most appropriate sampling procedure for this project and why?
    b) How would you choose the respondents if the chosen procedure was quota sampling?
  2. In the above example, the research committee is interested in the views of nurses to 'striking doctors'. Explain how the nurses will be chosen if theoretical sampling is employed.
  3. You have been appointed the chief researcher of a country town. Your task is to ascertain the attitudes of unmarried mothers to state policies relating to family allowances.
    a) Explain how you will choose the sample of mothers to address the research question, using a quantitative study.
    b) Explain how you will choose the sample of mothers to address the research question, using a qualitative study.
  4. As the research adviser of the educational division of the university you have been asked to investigate the views of students to the proposed increase in fees, which resulted from relevant government cuts. The sampling method you have been urged to use by the manager of the division is multi-stage sampling.
    a) Describe the steps you will employ to select your respondents by using this method.
    b) Discuss critically the suitability of such a sampling method in the context of the proposed study. Is this the sampling method you would have chosen if you had been free to decide on the matter?
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