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Paper IIIPaper IIIQualitative research

Qualitative research

methodologymethodology

Objective 1.5Objective 1.5

Discuss Discuss sampling techniques

sampling techniques appropriate to appropriate to

qualitative research.

qualitative research.

Sampling in Qualitative Sampling in Qualitative ResearchResearchWe will discuss We will discuss threethree of the of the most common sampling most common sampling methods used in qualitative methods used in qualitative research: research: 1. Purposive sampling1. Purposive sampling2. Snowball sampling.2. Snowball sampling.Sa

mpling

in Q

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tive

Rese

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• As defined by Kerlinger (1986), purposive sampling is another non-probability based sampling.

• It is characterized by a deliberate effort to obtain representative samples through the inclusion of groups or typical areas in a sample.

Wha

t is

purp

osiv

e

sam

plin

g?

• The researcher actively selects The researcher actively selects the most productive sample to the most productive sample to answer the research question.answer the research question.

• This can involve developing a This can involve developing a framework of the variables framework of the variables that might influence an that might influence an individual's contribution and individual's contribution and will be based on the will be based on the researcher's practical researcher's practical knowledge of the research knowledge of the research area, the available literature area, the available literature and evidence from the study and evidence from the study itself. itself.

Wha

t is

purp

osiv

e

sam

plin

g?

• Purposive sample sizes are Purposive sample sizes are often determined on the basis of often determined on the basis of theoretical saturation (the point theoretical saturation (the point in data collection when new in data collection when new data no longer bring additional data no longer bring additional insights to the research insights to the research questions).questions).

• Purposive sampling is therefore Purposive sampling is therefore most successful most successful when data when data review and analysis are done in review and analysis are done in conjunction with data collection. conjunction with data collection. W

hat i

s pu

rpos

ive

sam

plin

g?

• Purposive sampling design is usually used when a limited number of individuals possess the trait of interest.

• It is the only viable sampling technique in obtaining information from a very specific group of people.

Whe

n to

use

purp

osiv

e sa

mpl

ing?

• It is also possible to use purposive sampling if the researcher knows a reliable professional or authority that he thinks is capable of assembling a representative sample (this is a very subjective sample technique).

• The purposive sampling technique essentially is dependent upon the skill of the researcher to identify and find specific participants.

Whe

n to

use

purp

osiv

e sa

mpl

ing?

• In essence, In essence, subjects are selected because of some characteristic. Patton (1990) has proposed the following cases of purposive sampling:• Typical Case - Illustrates or highlights

what is typical, normal, average.• Extreme or Deviant Case - Learning

from highly unusual manifestations of the phenomenon of interest, such as outstanding success/notable failures, top of the class/dropouts, exotic events, crises.

• Convenience - Saves time, money, and effort. Poorest rational; lowest credibility. Yields information-poor cases.

Wha

t is

purp

osiv

e

sam

plin

g?

• Those who are unsuitable for Those who are unsuitable for the sampling study or who do the sampling study or who do not fit the bill have already been not fit the bill have already been eliminated, so eliminated, so only the most only the most suitable candidates remainsuitable candidates remain..

• As the most appropriate people As the most appropriate people for the study have been for the study have been selected, this process becomes selected, this process becomes a lot a lot less time consumingless time consuming..Ad

vant

ages

of

purp

osiv

e sa

mpl

ing

• The results of purposeful sampling are usually expected to be more representative of the population than those achieved with an alternative form of sampling.

• If you are looking for a If you are looking for a very rare very rare or much sought after group or much sought after group of of people for a particular research people for a particular research study, using purposive sampling study, using purposive sampling may usually be the may usually be the only way only way you can track them down.you can track them down.

Adva

ntag

es o

f

purp

osiv

e sa

mpl

ing

• Quite often Quite often market researchers market researchers use use this type of sampling in order to target this type of sampling in order to target a particular group of people. a particular group of people.

• Basing their results on what this group Basing their results on what this group has said, their findings will then be has said, their findings will then be used as a representation of the rest of used as a representation of the rest of the population.the population.

• Deciding in advance what group to Deciding in advance what group to target based on the types of results a target based on the types of results a company is expecting to find will help company is expecting to find will help them save costs and get the job done them save costs and get the job done as soon as possible. as soon as possible.

Adva

ntag

es o

f

purp

osiv

e sa

mpl

ing

• Quite often Quite often market researchers market researchers use use this type of sampling in order to target this type of sampling in order to target a particular group of people. a particular group of people.

• Basing their results on what this group Basing their results on what this group has said, their findings will then be has said, their findings will then be used as a representation of the rest of used as a representation of the rest of the population.the population.

• Deciding in advance what group to Deciding in advance what group to target based on the types of results a target based on the types of results a company is expecting to find will help company is expecting to find will help them save costs and get the job done them save costs and get the job done as soon as possible. as soon as possible.

Lim

itatio

ns o

f

purp

osiv

e sa

mpl

ing

• The selection criteria the researcher uses can be very arbitrary and are almost always subjective.

• The narrowness of the questions used will reflect the researcher's particular stance on a subject far more than a random sample.

Lim

itatio

ns o

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purp

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e sa

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• The sample population used may not necessarily be entirely the population that the researcher is trying to reach.

• As such, since such a small sample population is often used, a small variation in the sample will cause deviance in the results.

Lim

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• Snowball sampling is a non-probability Snowball sampling is a non-probability sampling technique that is used by sampling technique that is used by researchers to identify potential researchers to identify potential subjects in studies where subjects are subjects in studies where subjects are hard to locate.hard to locate.

• This type of sampling technique works like chain referral. After observing the initial subject, the researcher asks for assistance from the subject to help identify people with a similar trait of interest.Sn

owba

ll sa

mpl

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• The process of snowball sampling is much like asking your subjects to nominate another person with the same trait as your next subject.

• The researcher then observes the nominated subjects and continues in the same way until the obtaining sufficient number of subjects.

• The snowball sampling technique essentially is dependent upon the participants to identify and find specific participants.

Snow

ball

sam

plin

g

• The process of snowball sampling is much like asking your subjects to nominate another person with the same trait as your next subject.

• The researcher then observes the nominated subjects and continues in the same way until the obtaining sufficient number of subjects.

• The snowball sampling technique essentially is dependent upon the participants to identify and find specific participants.

Snow

ball

sam

plin

g

Snowball sampling

Snowball sampling

When can this type of

When can this type of

sampling be useful?

sampling be useful?

• If obtaining subjects for a study that wants to observe a rare disease, the researcher may opt to use snowball sampling since it will be difficult to obtain subjects.

• It is also possible that the patients with the same disease have a support group; being able to observe one of the members as your initial subject will then lead you to more subjects for the study.

• Snowball sampling is often used with focus groups in qualitative research methods. Ap

plic

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Snow

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Advantages of snowball technique…Advantages of snowball technique…•The chain referral process allows the The chain referral process allows the researcher to reach populations that are researcher to reach populations that are difficult to sample when using other sampling difficult to sample when using other sampling methods. methods. •The process is cheap, simple and cost-The process is cheap, simple and cost-efficient. efficient. •This sampling technique needs little planning This sampling technique needs little planning compared to other sampling techniques.compared to other sampling techniques.

Limitations of snowball technique…Limitations of snowball technique… •Representativeness Representativeness of the sample is of the sample is not not guaranteed. guaranteed. The researcher has no idea of the true The researcher has no idea of the true distribution of the population and of the sample. distribution of the population and of the sample. •Sampling bias is also a fear of researchers when using Sampling bias is also a fear of researchers when using this sampling technique. this sampling technique. •Initial subjects tend to nominate people that they know Initial subjects tend to nominate people that they know well. Because of this, it is highly possible that the well. Because of this, it is highly possible that the subjects share the same traits and characteristics, thus, subjects share the same traits and characteristics, thus, it is possible that the sample that the researcher will it is possible that the sample that the researcher will obtain is only a small subgroup of the entire population.obtain is only a small subgroup of the entire population.