Sampling

Question 1

What is random sampling?

Answer 1

This is where every member of the
population has an equal chance of being
selected. The easiest way to do this is to
place all the names (or allocate
numbers) from a target population into
a hat and draw out the required sample.
Computer programmes can also
generate random lists of participants in
an unbiased way

Question 2

What are the strength of random sampling?

Answer 2

Less biased as all
members of the target
population have an
equal chance of
selection.

Question 3

What are the limitations of random sampling?

Answer 3

May not be representative of the
population. It is possible, by chance, the
randomly selected sample is biased
anyway e.g. too many males.
• Relies on all the target population being
able to take part if selected.
• Need to have access to all names target
population.

Question 4

What is systematic sampling?

Answer 4

This method involves selecting every
nth participant from the list of available
participants, e.g. every 5th person from a
list of 50 participants.

Question 5

Strengths of systematic sampling

Answer 5

The only researcher
involvement is deciding
the sample size, it
reduces investigator
bias.

Question 6

Limitations of systematic sampling?

Answer 6

May not be representative of the
population. It is possible, by chance, the
systematically selected sample is biased
anyway e.g. too many males.
• Relies on all the target population being
able to take part if selected.
• Need to have access to all names target
population

Question 7

What is stratified sampling?

Answer 7

Subgroups within a population are identified
Participants are obtained from each of the strata in proportion to their occurrence in the population
Selection is done using random techniques

Question 8

What are the strengths of stratified sampling?

Answer 8

Avoids investigator bias as all the key characteristics of the population are present in sample

Can be generalised as it is representative

Question 9

Limitations of stratified sampling .

Answer 9

If all key features of population are not identified then sample may not be representative so it may not be generalisable

Very time consuming to identify subgroups and then select participants randomly

Need to know all the names of the target population

Question 10

What is opportunity sampling?

Answer 10

Approach anyone in the immediate area who happens to be available to ask to participate

Question 11

What are the strengths of opportunity sampling

Answer 11

Easiest method as you use the first participants you find which means less time to locate your sample

Question 12

Limitations of opportunity sampling

Answer 12

Unlikely to be representative of target population as sample is taken from a small part of the target population

Researcher may be consciously or unconsciously show bias in sample selection so limiting generalisability

Question 13

What is volunteer sampling ?

Answer 13

Advertisements are used to attract participants
The participants volunteer themselves , usually requires an incentive

Question 14

Strengths of volunteer sampling

Answer 14

Easy method as less initial work involved than in random sampling

Question 15

Limitations of volunteer sampling

Answer 15

Sample bias- only certain types of people are likely to volunteer
They are atypical respondents with characteristics not necessarily common of the population (more time to give, highly motivated )
Limits generalisability