1. Chapter 13 Sampling: quantitative and qualitative

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

3. Samples and populations
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 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.
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 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 & 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)
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 & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

16. 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 & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

17. 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 & 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
Percentages found from sample (‘results’)
Conf.
Interval
50%
40/60%
30/70%
20/80%
10/90%
5/95%
1/99%
Necessary sample sizes +1
9600
9216
8064
6144
3456
1824
380 +2
2400
2304
2016
1536
864
456 * +4
600
576
504
384
216
114 +8
150
144
126 96 53
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
Sample size % CI
Range, %
Comment
Survey with sample of 200
200
Bowling 20
+5.5
14.5 – 25.5
Ranges overlap
Tennis 30
+6.3
23.7 – 36.3
Survey with sample of 500
500
Bowling 20
+3.5
16.5 – 23.5
Ranges do not overlap
Tennis 30
+4.0
26.0 – 34.0
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% = Survey Cost = 200 x $20 = $5000
N = 1000 CI for 50% = 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)
Item
Source
Number
Population
Census
500,000
Sample
Survey
1,000
% visiting facility/year
12%
% confidence interval
Table 13.1
+ 2.0%
Estimated no. persons
12% of 500,000
60,000
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/year
2.5
Estimated total visits
Calc.: (12% of 500,000) x 2.5
150,000
CI in no. visits
Calc: (2% of 500,000) x 2.5
+25,000
CI in % visits
Cals.: (25,000/150,000) x 100
+16.7%
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)
Minimum sample size to achieve CI of +5% or +1% on a sample finding of 50%
+5%
+1%
Infinite
384
9602
5 million
9584
1 million
9511
500,000
9422
100,000
383
8761
50,000
381
8056
10,000
370
4899
5000
357
3288
1000
278
906
100 80 99
A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge

25. Actual # of users (counts) Sample does not reflect the pattern of use
Weighting (Tables 13.4 & 13.5)
Example: one survey at a site
Time
# of Interviews %
Actual # of users (counts)
9-11 am 10
22.2 25
5.7 pm 12
26.7
240
55.2 pm 11
24.4
110
25.3 pm 60
2.7
Total 45
100.0
435
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)
Time
No. of Interviews
No. of Users
Weighting Factors
Weighted Sample No.
Source:
Survey
Counts
B/A
CxA
9-11 am 10 25
2.5 pm 12
240
20.0 pm 11
110
10.0 pm 60
5.0
Total 45
435
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)
Method
Characteristics
Convenience
Conveniently located persons or organisations -
Criterion
Selected on key criterion - eg. age-group.
Homogeneous
Deliberately homogeneous group: eg. university-educated male cyclists aged
Opportunistic
Taking advantages of opportunities as they arise - eg. a major sporting event taking place locally.
Maximum variation
Deliberately studying contrasting cases. Opposite of 'homogeneous'.
Purposeful
Similar to 'criterion' but may involve other considerations, such as 'maximum variation', typicality.
Snowball
Interviewees source of suggestions for contacts.
Stratified purposeful
A range of cases based on set criteria, eg. representatives of a range of age-groups or nationalities.
A. J. Veal & S. Darcy (2014) Research Methods for Sport Studies and Sport Management: A practical guide. London: Routledge