Sampling methods: description & evaluation
- Sampling techniques are the ways in which a researcher obtains their sample, as follows in the table below:
|
Sampling Type |
Description |
Strengths |
Limitations |
|
Stratified |
Small-scale reproduction of the target population, dividing and categorising the population by characteristics important to the research (strata), e.g. age, gender, education etc. The population is sampled within each category proportional to the overall figure - if the whole population has 18% of people who are male aged 30-40, then the representative sample will have 18% of people who are male aged 30-40. |
The sample is representative of the target population. Easy to generalise as the sample is representative. Selection is unbiased as it is based on the subgroups in society. |
Knowing the subgroups and dividing the population into categories, then selecting participants to match these, can be very time-consuming. The researcher requires knowledge of the subgroups and categories of the population, which may not be available. |
|
Random |
Selecting participants so that everyone has a fair chance of being selected. This could be achieved by putting all names in a hat and then drawing out names at random or using a computer-generated method. |
Unbiased selection, meaning it is more likely to be a representative sample. As the results are fairly representative, it means the results can be generalised to the target population. |
Time consuming and impractical, it is not always possible to have all of the information on a target population, or for all of the target population to want to take part in the study. It may be non-representative as one gender could be selected randomly, which would not be a true representation of the target population. |
|
Systematic |
Selecting every nth person from a list to make a sample. The researcher has to calculate how many people they need to know which nth they need e.g. every 10th, 100th or 1000th on a register/database/roll etc. |
Unbiased selection, meaning it is more likely to be a representative sample. As the sample is likely to be reasonably representative it means that the results can be generalised to the target population. |
Not always truly unbiased as the selection process can interact with a hidden periodic trait, if every 10th person is a 19-year-old shop worker, then they would be the only people in the sample. It may be non-representative as one gender could be selected systematically, which would not be a true example of the target population. |
|
Opportunity |
Selecting those who are most convenient, willing and available to take part. This could be asking people who are shopping in a local mall at 11 am or university students who are present at one of the researcher’s lectures. |
Also known as ‘convenience sampling’ for a reason - an easy way to find participants. This is a time-efficient way of obtaining a sample. |
Cannot generalise as the sample is likely to be unrepresentative e.g. some university students could be in another lecture or at the library; people who are at work are unlikely to be shopping at 11 am. It is a self-selected sample as participants have the option to agree or decline to join in at the time of the study so the sample may end up with participants who share personality traits. |
Worked example
Here is an example of a question you might be asked on this topic - for AO2.
AO2: You need to apply your knowledge and understanding, usually referring to the ‘stem’ in order to do so (the stem is the example given before the question)
You have been asked to conduct an experiment into the effect of loud music on memory.
Question: Describe how you would obtain an opportunity sample to conduct this experiment.
You need to include:
- How and where you will find your participants
- One example of a question you would ask each person to gain their consent to take part in your experiment [4]
Model answer:
- I would use opportunity sampling by approaching sixth-form students at my college who are in the common room during the lunch hour.
- I would approach each student and ask them the following question: ‘Do you consent to take part in my experiment on memory which I will be conducting in 5 minutes in Room X?’
