gud

1. http://www.prernaindia.in/
Qualitative Research Workshop
Sample Size and Sampling Strategy
Dr. Manisha Gore

2. http://www.prernaindia.in/ 2

3. http://www.prernaindia.in/ 4

4. http://www.prernaindia.in/
Maximum Variation Sampling
• Cases represent variations on specified aspects of a phenomenon of interests (eg. geographical
variations, education etc.)
• Capture and describe central themes that cut across variation (common pattern among variation)
• Results in high-quality, detailed description of each cases and important shared patterns.
• Evaluating the Essential New-born Care (ENC) programme in districts in India. Sampling could be
mothers with children less than 5 years. Select sites representing geographical variations Eg sites in
rural, urban, semi-urban.
6

5. http://www.prernaindia.in/
Extreme or Deviant Case Sampling
• Learning from highly unusual manifestations of the phenomenon of interest
• Selection of cases departing from a specified standard (unusual or special in some way)
• Aim is to study these cases that are relevant to improving typical cases
• Coping with life after HIV diagnosis in individuals infected with HIV. Sample would include HIV positive
individual affiliated to networks
7

6. http://www.prernaindia.in/
Homogeneous Sampling
• Selecting similar types to describe a particular group in-depth
• Selection of participants who have similar demographic characteristics age, gender, education etc.
• To understand menstruation hygiene practices of female adolescents studying in 8-10 stds of
government schools of rural areas
8

7. http://www.prernaindia.in/
Convenience Sampling
• Convenience sampling defined as individuals believed to be representative of the population from which
they are selected, but chosen because they are close at hand and easy to get access to them rather than
being randomly selected. e.g. when you simply ask any patient in your clinic who is willing to participate.
• Convenience sampling saves time, money, and effort, but it is the least rigorous technique and may
result in poor quality data and lacks intellectual credibility. There is an element of convenience sampling
in many qualitative studies, but a more thoughtful approach to selection of a sample is usually justified.
• Clinicians selecting patients as respondents coming to their clinics
9

8. http://www.prernaindia.in/
OPPORTUNISTIC OR EMERGENT SAMPLING
• New opportunities to recruit participants or to gain access to a new site may develop after the fieldwork
has begun.
• For example a researcher studying heart attacks may, for example, meet a cardiologist while
interviewing one of his or her patients. The cardiologist may suggest how the researcher can contact
other cardiologists who would be willing to refer clients to the researcher.
10

9. http://www.prernaindia.in/
CRITERION SAMPLING
• All cases that meet a set of criteria are selected. In criterion sampling it is important to select the criteria
carefully, so as to define cases that will provide detailed and rich data relevant to the particular research
problem.
• Cases that provide important qualitative component to the study
• For example, all former clients of an intensive care unit who return to intensive care with the same
complaint within three weeks may constitute a sample for in-depth, qualitative study. These criteria
would facilitate a study of the effectiveness of after-care programs attached to intensive care units.
11

10. http://www.prernaindia.in/
CONCLUSION FLEXIBILITY IN QUALITATIVE SAMPLING
• A flexible research and sampling design is an important feature of qualitative research, particularly
when the research being conducted is exploratory in nature.
• When little is known about a phenomenon or setting, a priori sampling decisions can be difficult. In such
circumstances, creating a research design that is flexible enough to foster reflection and preliminary
analysis may be a good idea.
13

11. http://www.prernaindia.in/
Sample Size
“ Determining adequate sample size in qualitative research is ultimately a
matter of judgement and experience”- (Sandolweski,1995).
14

12. http://www.prernaindia.in/
Factors of Sample Size
• Theoretical Saturation
• In their original treatise on grounded theory, Glaser and Strauss (1967: p. 61) defined
saturation in these terms:
“The criterion for judging when to stop sampling the different groups means that no
additional data are being found whereby the sociologist can develop properties of the
category. As he sees similar instances over and over again, the researcher becomes
empirically confident that a category is saturated. He goes out of his way to look for
groups that stretch diversity of data as far as possible, just to make certain that saturation
is based on the widest possible range of data on the category.”
16

13. http://www.prernaindia.in/
….cont.
• Sample should be large enough to make meaningful comparisons in relations to research questions.
• Number of comparison groups (more comparisons-larger sample size)
• Detail, complexity and depth (more detailed, complex, and in-depth-smaller sample size)
• Develop explanations to account for similarities & differences in particular contexts.
17

14. http://www.prernaindia.in/
….cont
• Sampling to point of redundancy, an ideal
• More practical suggestion- use judgement and negotiation
• Specify minimum sample size based on study purpose and build a rationale
• Design should be understood to be flexible
• Exercise care not to over-generalize
18

15. http://www.prernaindia.in/
• THANK YOU
19