DEFINITION
OF SAMPLE
The sample method involves taking a
representative selection of the population and using the data collected as
research information. A sample is a “subgroup of a population”. It has also
been described as a representative “taste” of a group The sample should be
“representative in the sense that each sampled unit will represent the
characteristics of a known number of units in the population” The standard
definition always includes the ability of the research to select a portion of
the population that is truly representative of said population.
PROBABILITY
SAMPLING
Probability sampling is sometimes called
random sampling. Probability sampling provides an advantage because of
researcher’s ability to calculate specific bias and error in regards to the
data collected. Probability sampling is defined as having the “distinguishing
characteristic that each unit in the population has a known, nonzero
probability of being included in the sample”. It is described more clearly as
“every subject or unit has an equal chance of being selected” from the
population. It is important to give everyone an equal chance of being selected
because it “eliminates the danger of researchers biasing the selection process
because of their own opinions or desires”.When bias is eliminated, the results
of the research may be generalized from the sample to the whole of the
population because “the sample represents the population”
TYPES
OF PROBABILITY SAMPLING
Simple:
Each member of the study population has an equal probability of being selected.
Systematic:
Each member of the study population is either assembled or listed, a random
start is designated, then members of the
population are selected at equal intervals
Stratified:
Each member of the study population is assigned to a group or stratum, then a
simple random sample is selected from each stratum.
Cluster:
Each member of the study population is assigned to a group or cluster, then
clusters are selected at random and all members of a selected cluster are
included in the sample.
NON-PROBABILITY
SAMPLING
Non-probability
sampling is sometimes called non-random sampling. Non-probability sampling is a
good method to use when conducting a pilot study, when attempting to question
groups who may have sensitivities to the questions being asked and may not want
answer those questions honestly, and for those situations when ethical concerns
may keep the researcher from speaking to every member of a specific group. Non-probability
sampling is a good method to use when conducting a pilot study, when attempting
to question groups who may have sensitivities to the questions being asked and
may not want answer those questions honestly, and for those situations when
ethical concerns may keep the researcher from speaking to every member of a
specific group.
NON-PROBABILITY
SAMPLING METHODS
Convenience: Select cases based on their availability for the
study.
Purposive: Select cases that judged
to represent similar characteristics.
Snowball: Group members identify
additional members to be included in the sample.
Quota: Interviewers select a sample
that yields the same proportions as the population proportions
on easily identified variable
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