Sampling Methods Flashcards
What is random sampling
This method gives every member of the target group an equal chance of being selected for the sample
(e.g. by assigning a number to each member, and then selecting from the pool at using a random number generator).
What is the strengths of random sampling
-It is widely accepted that since each
member has the same probability of being
selected, there is a reasonable chance of
achieving a representative sample.
What are the weaknesses of random sampling
-Small minority groups within your target
group may distort results, even with a
random sampling technique.
-It can be impractical (or not possible) to use
a completely random technique, e.g. the
target group may be too large to assign
numbers to.
What is systematic sampling
A systematic method is chosen for selecting from a target group
(e.g. every fourth person in a list could be used in the sample. It differs from random sampling in that it does not give an equal chance of selection to each individual in the target group.)
What is the strength of systematic sampling
-Assuming the list order has been
randomized, this method offers an
unbiased chance of gaining a
representative sample.
What is the weakness of systematic sampling
-If the list has been assembled in any other
way, bias may be present. For example if
every fourth person in the list was male,
you would have only males in your sample.
What is stratified sampling
Here the sampler divides or ‘stratifies’ the target group into
sections, each showing a key characteristic which should be
present in the final sample. Then each of those sections is
sampled individually. The sample thus created should
contain members from each key characteristic in a
proportion representative of the target population.
What is the strength of stratified sampling
-It avoids the problem of misrepresentation sometimes
caused by purely random sampling.
What are the weaknesses of stratified sampling
-It takes more time and resources to plan.
Care must be taken to ensure each key characteristic
present in the population is selected across strata,
otherwise this will design a biased sample.
What is opportunity sampling
Participants who are both accessible and willing to take part are targeted
(e.g. employees from a conveniently located employer near the laboratory could be selected for the sample group.)
What is the strength of opportunity sampling
-This method is easy and inexpensive to carry out.
What is the weaknesses of opportunity sampling
-The consequent sample may not be representative as it
could be subject to bias
(e.g. the conveniently located employer may undertake a selection process for job applicants, making it likely that employees possess certain similar characteristics that are unrepresentative of the wider target group).
What is the volunteer sampling
Here the sample consists of people who have volunteered to be in the study.
What is the strengths of volunteer sampling
-This often achieves a large sample size through reaching a
wide audience, for example with online advertisements.
What is the weakness of volunteer sampling
-Those who respond to the call for volunteers may all display
similar characteristics (such as being more trusting or
cooperative than those who did not apply) thus increasing
the chances of yielding an unrepresentative sample.
