Chapter 13 Sampling: quantitative and qualitative

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<ul><li> Slide 1 </li> <li> Chapter 13 Sampling: quantitative and qualitative </li> <li> Slide 2 </li> <li> CONTENTS Samples and populations Representativeness Sample size Weighting Sampling for qualitative research </li> <li> Slide 3 </li> <li> 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: 1.What procedures must be followed to ensure that the sample is representative of the population? 2.How large should the sample be? A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 4 </li> <li> 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 5 </li> <li> 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 1.Select states/regions 2.Within state/region select local government areas (lga) or constituencies/electorates 3.Within lgas or constituencies/electorates for face-to-face interviews select streets (telephone surveys select numbers at this point) 4.Select clusters of 10-15 houses A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 6 </li> <li> 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 7 </li> <li> Sampling for site/user/visitor surveys 1. ISUM: Interviewer stationary user mobile: eg. interviewing at entrance/exit Sample by selecting: next person to pass entrance/exit point 2.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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 8 </li> <li> 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 9 </li> <li> Sampling for mail surveys Sample from mail-out list 100% sample often used A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 10 </li> <li> 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 11 </li> <li> 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.orgwww.random.org A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 12 </li> <li> Sample size Required sample size is not related to population size (except for small populations see later) Criteria: o The required level of precision in the results o The level of detail in the proposed analysis o The available budget A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 13 </li> <li> 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 range either 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 14 </li> <li> Normal curve (Fig. 13.1) A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 15 </li> <li> Confidence intervals (CIs) (Table 13.1: Extract) Sample size (N) Percentages found from sample (results) 50%40/60%30/70%20/80%10/90%5/95%2/98%1/99% Confidence intervals (CIs) + % 500+4.4+4.3+4.0+3.5+2.6+1.9+1.2+0.9 A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 16 </li> <li> Confidence intervals (CIs) (Table 13.1) Sample size (N) Percentages found from sample (results) 50%40/60%30/70%20/80%10/90%5/95%2/98%1/99% Confidence intervals (CIs) + % 500+4.4+4.3+4.0+3.5+2.6+1.9+1.2+0.9 So CI for 20% finding is 30% +4.0 = a range of: 26.0% to 34.0%. CI is not related to population size. NB. CI for p = CI for 100-p eg. CI is the same for 40% and 60% CI for 50% is the largest in absolute terms This table refers to 95% probability CIs others can be calculated eg. 99% A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 17 </li> <li> Confidence intervals (CIs) contd (Table 13.1) Sample size (N) Percentages found from sample (results) 50%40/60%30/70%20/80%10/90%5/95%2/98%1/99% Confidence intervals (CIs) + % 500+4.4+4.3+4.0+3.5+2.6+1.9+1.2+0.9 2000+ 2.2+2.1+2.0+1.7+1.3+1.0+0.6+0.4 So to halve the CI it is necessary to increase the sample fourfold. A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 18 </li> <li> 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 Percentages found from sample (results) Conf. Interval 50%40/60%30/70%20/80%10/90%5/95%1/99% Necessary sample sizes +1+1960092168064614434561824380 +2+22400230420161536864456* +4+4600576504384216114* +8+81501441269653** A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 19 </li> <li> 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 20 </li> <li> Detail of proposed analysis Sample size %CIRange, %Comment Survey with sample of 200 200Bowling20+5.514.5 25.5Ranges overlap Tennis30+6.323.7 36.3 Survey with sample of 500 500Bowling20+3.516.5 23.5Ranges do not overlap Tennis30+4.026.0 34.0 A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 21 </li> <li> 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 22 </li> <li> Confidence intervals and population estimates (Table 13.3) ItemSourceNumber PopulationCensus500,000 SampleSurvey1,000 % visiting facility/yearSurvey12% % confidence intervalTable 13.1+ 2.0% Estimated no. persons12% of 500,00060,000 CI in no. persons+ 2% of 500,000+ 10,000 CI as % of persons(10,000/60,000) x 100+ 16.7% Frequency of visit/yearSurvey2.5 Estimated total visitsCalc.: (12% of 500,000) x 2.5150,000 CI in no. visitsCalc: (2% of 500,000) x 2.5+25,000 CI in % visitsCals.: (25,000/150,000) x 100+16.7% A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 23 </li> <li> Sampling for small populations CIs are affected by population size if population is below about 50,000 See Table 13.3 A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 24 </li> <li> Sample size &amp; population size: small popns (Table 13.3) Population sizeMinimum sample size to achieve CI of +5% or +1% on a sample finding of 50% +5%+1% Infinite3849602 5 million3849584 1 million3849511 500,0003849422 100,0003838761 50,0003818056 10,0003704899 50003573288 1000278906 1008099 A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 25 </li> <li> Weighting Weighting (Tables 13.4 &amp; 13.5) Time# of Interviews %Actual # of users (counts) % 9-11 am1022.2255.7 11.01-1 pm1226.724055.2 1.01-3 pm1124.411025.3 3.01-5 pm1226.7602.7 Total45100.0435100.0 Sample does not reflect the pattern of use Example: one survey at a site A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 26 </li> <li> Weighting contd (Table 13.5) ABCD TimeNo. of Interviews No. of UsersWeighting Factors Weighted Sample No. Source:SurveyCountsB/ACxA 9-11 am10252.525 11.01-1 pm1224020.0240 1.01-3 pm1111010.0110 3.01- 5pm12605.060 Total45435 A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 27 </li> <li> 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 &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> <li> Slide 28 </li> <li> MethodCharacteristics ConvenienceConveniently located persons or organisations - Sampling for qualitative research contd (Table 13.6) CriterionSelected on key criterion - eg. age-group. HomogeneousDeliberately homogeneous group: eg. university- educated male cyclists aged 20-30. OpportunisticTaking advantages of opportunities as they arise - eg. a major sporting event taking place locally. Maximum variationDeliberately studying contrasting cases. Opposite of 'homogeneous'. PurposefulSimilar to 'criterion' but may involve other considerations, such as 'maximum variation', typicality. SnowballInterviewees source of suggestions for contacts. Stratified purposefulA range of cases based on set criteria, eg. representatives of a range of age-groups or nationalities. A. J. Veal &amp; S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge </li> </ul>

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