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Chapter 13 Sampling: quantitative and qualitative

Chapter 13 Sampling: quantitative and qualitative. CONTENTS. Samples and populations Representativeness Sample size Weighting Sampling for qualitative research. Samples and populations. Population:

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Chapter 13 Sampling: quantitative and qualitative

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  1. Chapter 13 Sampling: quantitative and qualitative

  2. CONTENTS • Samples and populations • Representativeness • Sample size • Weighting • Sampling for qualitative research

  3. Samples and populations • Population: • Total category of subjects that is the focus of attention in a particular research project (can be non-human) • Sample: • A number of subjects drawn from the population • Two key issues: • What procedures must be followed to ensure that the sample is representative of the population? • How large should the sample be? A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  4. Representativeness • Achieved by Random sampling: • A systematic selection process which ensures that all members of the population have an equal chance of inclusion in the sample • Designed to ensure representativeness • An unrepresentative sample is:biased • How is random sampling achieved in practice? A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  5. Sampling for household surveys • Ideally • Eg. 10 million population – sample of 1000: all 10 m. names put in a drum and 1000 drawn. • In practice: • For national/regional surveys – multi-stage sampling used • Select states/regions • Within state/region select local government areas (lga) or constituencies/electorates • Within lgas or constituencies/electorates for face-to-face interviews select streets (telephone surveys select numbers at this point) • Select ‘clusters’ of 10-15 houses A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  6. Sampling for telephone surveys • Telephone numbers selected at random from telephone directory • For large-scale surveys: automated by Computer-Aided telephone Interviewing (CATI) • Requires access to electronic directory with residential/business numbers identified • No directories for mobile phones • For household and telephone surveys: select person in household randomly: eg person with next birthday A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  7. Sampling for site/user/visitor surveys • ISUM: Interviewer stationary – user mobile: • eg. interviewing at entrance/exit • Sample by selecting: ‘next person to pass entrance/exit point • USIM: User stationary – interviewer mobile • eg. interviewing people on a beach • Interviewers should have a set route/rules to follow – eg. ‘interview every third person/group’ 3. Handouts • Handing out questionnaires to (all) visitors for self-completion • Not generally recommended unless closely supervised – generally very poor response rates A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  8. Sampling for street/quota surveys • Can be used when data are available on key characteristics of population: • age/sex structure of a community – from Census • Interviewing target numbers determined by population characteristics • Eg. if Population Census indicates 12% retired: if overall sample size is 200: interview 24 retired people A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  9. Sampling for mail surveys • Sample from mail-out list • 100% sample often used A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  10. Sampling for complex events and destination surveys • Different components will conform to above guidelines – mostly site surveys • Problem lies in combining data from different sources for an overall result, if required. A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  11. Sampling/ random assignment for experimental research • Samples of subjects often ‘convenience’ samples – eg. Students • Assignment to control and experimental groups: • Use of random numbers • Online: eg. www.random.org A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  12. Sample size • Required sample size is not related to population size (except for small populations – see later) • Criteria: • The required level of precision in the results • The level of detail in the proposed analysis • The available budget A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  13. Level of precision – confidence intervals • A statistic (finding) from a sample survey is an estimate of the population statistic • In a randomly drawn sample the sample value has a certain probability of being in a certain rangeeither side of the population value • Eg. 95% probability of being within 2 ‘standard errors’ • See ‘Normal distribution’ • Theoretical: imagine drawing lots of samples: some would be accurate, some not • Discussed further in Ch. 17 A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  14. Normal curve (Fig. 13.1) A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  15. Confidence intervals (CIs) (Table 13.1: Extract) A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  16. Confidence intervals (CIs) (Table 13.1) A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  17. Confidence intervals (CIs) contd(Table 13.1) So to halve the CI it is necessary to increase the sample fourfold. A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  18. Confidence intervals (CIs) contd(Table 13.2) Table 13.1 can be changed to present necessary sample size for a given CI – see Table 13.2 A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  19. Suggested appendix on sample size and CIs • See Appendix 13.1 • table indicating levels of Cis • statement indicating that they have been taken into account A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  20. Detail of proposed analysis A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  21. Budget • Key issue: halving the CI requires 4-fold increase in sample size • Eg. N = 250 CI for 50% = +6.2 Survey Cost = 200 x $20 = $5000 N = 1000 CI for 50% = +3.1 Survey Cost = 1000 x $20 = $20,000 • If resources not available for adequate sample size, consider: • Pilot/exploratory study • Qualitative study A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  22. Confidence intervals and population estimates (Table 13.3) A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  23. Sampling for small populations • CIs are affected by population size if population is below about 50,000 • See Table 13.3 A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  24. Sample size & population size: small pop’ns(Table 13.3) A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  25. Weighting(Tables 13.4 & 13.5) Example: one survey at a site Sample does not reflect the pattern of use A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  26. Weighting contd(Table 13.5) A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  27. Sampling for qualitative research • Number of subjects generally be small, but: • sampling process is still important • should be fully described in research report • A range of approaches is possible A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

  28. Sampling for qualitative research contd(Table 13.6) A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

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