A target population is a group of people that share a set of characteristics about which a researcher wishes to draw conclusions.
The sample (small selection of the target population) should be representative in that they share all the important characteristics of the rest of the target population.
A sampling method refers to the way in which the participants are selected to take part in research.
Each method has its advantages and disadvantages which psychologists must be aware of as these may affect their research findings.
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Opportunity Sampling
An opportunity sample involves the researcher selecting anyone who is available and willing to take part in reseach.
Advantage: Quick and easy to obtain so large number of participants can be recruited without too much effort so often more practical as results can be obtained faster.
Disadvantage: Participants are likely to have a similar background so the results are less likely to be generalisable to the wider population.
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Volunteer Sampling
Sometimes referred to as self-selecting sample, this involves participants selecting themselves, often through replying to an advertisement and volunteering to take part in research.
Advantage: Useful when the research requires specific type of participants. Also, anyone can apply to participate so could be considered random and therefore generalisable.
Disadvantage: Can be expensive and requires a lot of effort. Also, the findings might be biased as only certain types of people are likely to apply, therefore not generalisable.
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Random Sample
In a random sample, every person in a given target population stands an equal chance of being selected for inclusion. Collate the names of all the possible participants and using a random number generator select enough participants to make up the sample.
Advantage: Most representative as everyone has an equal chance of participating, so the findings will be generalisableto the wider population. The sample will have population validity as it is measuring the people it intended to measure.
Disadvantage: Unless the target population is small it is very difficult to obtain a list of all the people who would be required. More expensive and time consuming so not often used
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Stratified Sample
This involves a selection of certain groups in a way that will match the variety and proportion in which participants occur amongst the general population. E.G= if 40% of psychology students are males,then a stratified sample should include 40% of males.
Advantage: Ensures that different groups are represented so conclusions about differences between those groups could be drawn and findings generalised to the wider population.
Disadvantage: Difficult to establish the exact numbers of people in each group to ensure proportional representation and especially if actual group size is very small so the findings may not be generalisable to the wider population.
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