MET Sampling Flashcards
Population definition
Who the study is about and who the results apply to
Who the sample is chosen from
Sample definition
People who take part in a study - the participants
What should participants be?
Representative of the population
What is a representative sample? What does this mean the results are?
Consists of a selection of typical members of the population
Generalisable - what is true of sample is true of population
What is a biased sample?
Over or under represents certain groups or characteristics
Not representative of population
Results cannot be generalised to population
What is random sampling? What is quasi-random sampling? What two random sampling techniques are there?
Process of choosing participants involves only random process
Quasi-random sampling includes stratified and systematic sampling - because the pps are obtained from a list not the full actual population
Computer method - allocate each name a number, use a randomised program to select N numbers, pps are those numers are chosen
Manual method - put each name on paper in container, choose N pieces of paper, pps are those whose names are chosen
Strengths and limitations of random sampling
Strengths - best probability of representative sample, taking choice out of researcher’s control eliminates bias
Limitations - sample could be unrepresentative of some groups by chance / random error
What is stratified sampling?
Sampling population identified, appropriate strata/groups divide sample, proportions needed for representative group identified, random sampling used to choose the appropriate N from each strata
Strata used should be ones that might affect results
What is systematic sampling?
Specify population, identify sampling population
Work out proportion of sampling population for N
Choose every nth member of the sample
Commonly done to avoid time-consuming random sampling, or awkward practical issues such as fast cars going past
What is opportunity sampling?
Use whoever is available
For example - Unis - use own students
What is volunteer sampling?
Recruit via advertisements online/public places
Volunteers come forward
Strengths and limitations of stratified sampling
Strengths - more likely to be representative
Limitations - time consuming
Strengths and limitations of systematic sampling
Strengths - more practical than random, likely to be representative
Limitations - small chance of systematic error
Strengths and limitations of opportunity and volunteer sampling
Strengths - less time consuming, no need for sampling population
Limitations - less likely to representative, especially volunteers as they are more likely to be parts of certain groups or have certain characteristics
