This document discusses various sampling strategies used in qualitative research including:
1) Purposeful sampling is used to select information-rich cases to answer research questions, such as extreme or typical cases.
2) Specific purposeful sampling strategies are described like maximum variation which selects cases from different conditions, and homogeneous groups which provides an in-depth look at a subgroup.
3) Other strategies discussed include snowball sampling which asks participants who else to interview, criterion sampling which uses predetermined criteria, and opportunistic sampling which makes on-the-spot decisions in the field.
Purposeful sampling strategies
•Extreme cases
(outliers)
• Maximum variation
• Homogeneous groups
• Typical/average case
• Critical case
• Snowball
• Criterion
• Theory-based
• Confirming &
disconfirming cases
• Stratified purposeful
• Opportunistic/emergen
t
• Purposeful random
5.
Extreme cases /outliers
• Cases that have gone extremely well or extremely wrong
– i.e. excellence or extreme failure
• Illuminative of other, less extreme instances
6.
Maximum variation sampling
•Pick a few cases from different conditions: eg:
• very poor, middle class, very rich
• very large, medium, small (town, class, college)
• Identify shared patterns across these variations
7.
Homogeneous groups
• Smallgroup of similar cases to describe in depth
• Used to gain information about a particular subgroup (i.e.
single dads)
• Used in focus group research
8.
Typical/average case
• Identifiedwith the help of key informants or previous
research
• What criteria do you use to define typical?
• e.g. Typical science classroom/prof
9.
Critical case sampling
•If it happens here, it will happen everywhere
• e.g. if conservative group adopts new technology, every
other group will
10.
Snowball / chainsampling
• Ask participants: who should I talk to? Who knows a lot
about… Who does… ?
11.
Criterion sampling
• Participantsmust meet certain criteria
• EG:
• age requirements
• weekly users of Facebook, Twitter, AND LinkedIn
• teach mathematics at x level
12.
Theory based sampling
•A type of criterion sampling
• The criteria are derived from theory
• EG:
• early adopters (diffusion of innovations)
• high communication apprehension
• spatial learners
13.
Confirming & disconfirmingcases
• Confirming cases support your analysis
• Disconfirming cases contradict your analysis, prompt you
to look for alternate explanations
• Used later in the research process, after patterns have
emerged
• EG
• non-traditional students who do learn better when using the Smart
Pen
• non-traditional students who perform worse when using the Smart
Pen
Purposeful random sampling
•Used to select a small number of cases to study from a
large pool of available cases that qualify
• EG:
• typical case sampling: pick 5 out of 50 cases
17.
Sample size inqualitative research
• Sample to the point of redundancy
• For IRB purposes, specify a safely large number