Sampling Flashcards
(7 cards)
Population and sampling
Population = large group of individuals that a R wants to study
Target population = subset of the general population
Researcher then selects a smaller group = sample
- the sample is representative of the target population - so it can be generalised
Random sample + evaluate
- all the members of the target population have an equal chance of being selected
- use the lottery method; give people number and select at random
-> unbiased; confounding and extraneous V equally divided between groups = internal validity
-> difficult and time consuming
-
Systematic sample + evaluate
- every nth member of the target population is selected e.g. every 3rd house on the street
- sampling frame is produced - list of people are organised
-> objective
-> method is time consuming so pts may refuse to take part
-> sample may still be unrepresentative
Stratified sample
- the composition of the sample reflects the proportions of people in certain groups (strata) within the target population
1. Identify the different strata of the population
2. Proportions of the sample are worked out
3. Pts make up each strata + selected via random sampling
Opportunity sampling + evaluate
- researcher selects anyone who is willing and available
-> takes less time and money
-> sample is unrepresentative of the target pop, as it is drawn from a specific area - findings cant be generalised
-> R has complete control over the selection of pts = researcher bias
Volunteer sample + evaluate
- pts select themselves to be part of the sample
- e.g. researcher may put an add in the newspaper
-> minimal inputs from the R; less time consuming
-> pts more engaged
-> volunteer bias; attract a certain ‘profile’ of person, tries to please the R.
Evaluate stratified sampling
-> representative sample, designed to accurately reflect the composition of the population - can generalise the findings
-> complete representation is not fully possible
