research methods - sampling. Flashcards
What is meant by “target population”?
A large group of individuals a researcher is interested in studying such as the effects of antidepressants on individuals diagnosed with depression.
What is meant by “sample”?
A sub-group of the target population and they take part in the investigation which should be representative of the target population.
What is meant by “sampling technique”?
Method use to select people from a population.
What is meant by “random sampling”?
Sampling technique where every member of the population has an equal chance of being chosen.
What is meant by “systematic sampling”?
Using a predetermined system to select participants from a population such as selecting every nth person from the population where the numerical interval is applied consistently.
What is meant by “stratified sampling”?
Classifying the population into subgroups (strata) and then choosing a sample which consists of participants from each strata in the same proportions as they occur in the population.
What is meant by “opportunity sampling”?
Sampling technique where researchers select anyone who is available at the time the study is carried out and fit the criteria being looked for.
What is meant by “volunteer sampling”?
Participants select themselves to be part of the sample where researchers normally place an advert in a newspaper or place notices.
What are the sampling techniques?
- random.
- systematic.
- stratified.
- opportunity.
- volunteer.
What are the strengths of opportunity sampling?
- easy.
- inexpensive.
- less planning and preparation required leading to few delays in research process and less money.
What is a weakness of opportunity sampling?
- may not be representative therefore sample may not be generalised lacking population validity.
What is a strength of random sampling?
- chance of achieving representative sample due to each member having the same probability of being picked.
What are the weaknesses of random sampling?
- difficult to obtain and time consuming where target population may be too large.
- may end up with an unrepresentative sample such as picking all females.
- selected participants may refuse to take part.
What are the strengths of stratified sampling?
- avoids the problem of malpresentation sometimes caused by purely random sampling.
- likely to have high population validity as there is an equal chance for everyone to be picked.
- more representative of target population.
What are the weaknesses of stratified sampling?
- takes more time and resources to plan which may cause delays.
- care must be taken to ensure each key characteristic present in the population is selected across the strata otherwise this will design a biased sample.
What are the strengths of systematic sampling?
- objective and avoids researcher bias as researcher has no influence over who is chosen.
- chance of more representative sample.
What is a weakness of systematic sampling?
- if list is assembled in any other way bias may be present such as if every 4th person was a male it would create an unrepresentative sample.
What are the strengths of volunteer sampling?
- achieves a large sample size through reaching a wide audience such as online adverts.
- quick, convenient and economical as there is less planning and preparation required so fewer delays in research and less money spent.
What is a weakness of volunteer sampling?
- volunteer bias where those volunteering may be more motivated or have more free time producing an unrepresentative sample.
How is random sampling done?
- by having a list of all members in the target population
- each name is assigned to a number
- sample is generated using a lottery method (computer-based randomiser or picking numbers from a hat).
