Sample selection and techniques

Question 1

What is opportunity sampling?

Answer 1

The sample is those members of the target population who happen to be available at the time.
It’s the best when your target population is gathered together in a location where you can approach a varied selection of them.

Question 2

What is volunteer sampling?

Answer 2

The sample is those members of the target population who select themselves.
It’s the best when your target population is likely to read the same magazine or newspaper, visit the same website or look at the same noticeboard.

Question 3

What is random sampling?

Answer 3

The sample is members of the target population selected without any bias.
It’s the best when your target population isn’t too large and you can get hold of a “master list” of all the members.

Question 4

What is stratified sampling?

Answer 4

The sample is members of the target population selected in an unbiased way but guaranteed to be representative in certain ways.
Strata are sub-groups within the target population. This technique involves working out the strata you need in your sample and how many people there should be in each, then filling the strata through random sampling.
It’s the best when you have what you need for random sampling and also the topic you are researching suggests a small number of very obvious strata.

Question 5

What are the strengths of each sampling technique?

Answer 5

Opportunity - quick and convenient
Volunteer - no experimenter bias
Random - no bias at all
Stratified - no bias at all, representative of strata used

Question 6

What are the weaknesses of each sampling technique?

Answer 6

Opportunity - experimenter bias, may be representative
Volunteer - slow and inconvenient, may be unrepresentative
Random - slow and inconvenient, may be unrepresentative
Stratified - very slow and inconvenient, may ignore important strata