Sampling
techniques: Advantages and disadvantages
|
Technique
|
Descriptions
|
Advantages
|
Disadvantages
|
|
Simple random
|
Random sample from
whole population
|
Highly representative
if all subjects participate; the ideal
|
Not possible without
complete list of population members; potentially uneconomical to achieve; can
be disruptive to isolate members from a group; time-scale may be too long,
data/sample could change
|
|
Stratified random
|
Random sample from
identifiable groups (strata), subgroups, etc.
|
Can ensure that specific
groups are represented, even proportionally, in the sample(s) (e.g., by
gender), by selecting individuals from strata list
|
More complex, requires
greater effort than simple random; strata must be carefully defined
|
|
Cluster
|
Random samples of
successive clusters of subjects (e.g., by institution) until small groups are
chosen as units
|
Possible to select
randomly when no single list of population members exists, but local lists
do; data collected on groups may avoid introduction of confounding by isolating
members
|
Clusters in a level
must be equivalent and some natural ones are not for essential
characteristics (e.g., geographic: numbers equal, but unemployment rates
differ)
|
|
Stage
|
Combination of cluster
(randomly selecting clusters) and random or stratified random sampling of
individuals
|
Can make up probability
sample by random at stages and within groups; possible to select random
sample when population lists are very localized
|
Complex, combines
limitations of cluster and stratified random sampling
|
|
Purposive
|
Hand-pick subjects on
the basis of specific characteristics
|
Ensures balance of
group sizes when multiple groups are to be selected
|
Samples are not easily
defensible as being representative of populations due to potential
subjectivity of researcher
|
|
Quota
|
Select individuals as
they come to fill a quota by characteristics proportional to populations
|
Ensures selection of
adequate numbers of subjects with appropriate characteristics
|
Not possible to prove
that the sample is representative of designated population
|
|
Snowball
|
Subjects with desired
traits or characteristics give names of further appropriate subjects
|
Possible to include
members of groups where no lists or identifiable clusters even exist (e.g.,
drug abusers, criminals)
|
No way of knowing
whether the sample is representative of the population
|
|
Volunteer, accidental,
convenience
|
Either asking for
volunteers, or the consequence of not all those selected finally
participating, or a set of subjects who just happen to be available
|
Inexpensive way of ensuring
sufficient numbers of a study
|
Can be highly
unrepresentative
|
Source: Black, T. R. (1999). Doing quantitative research in the social sciences: An integrated
approach to research design, measurement, and statistics. Thousand Oaks, CA:
SAGE Publications, Inc. (p. 118)
