Sampling Methods in Sociological Research
A sample is a smaller group selected from the target population that the sociologist actually collects data from, since studying an entire population is rarely practical. A sampling frame is the list of every member of the target population from which a sample is drawn, such as a school roll or the electoral register.
Before you start
Make sure you're comfortable with these topics first:
Method
- Identify whether the question asks you to name a sampling technique, describe it, or evaluate it against the needs of a specific study.
- Know the technical difference between a sampling frame, the full list, and a sample, the people actually selected from it.
- Match the technique to the population: snowball sampling for a hidden or hard-to-access group, stratified sampling when the sample must mirror the wider population's proportions accurately, systematic sampling when there is a large, orderly sampling frame, and opportunity sampling when time or money are very limited.
- When evaluating a technique, link it back to representativeness: does it give every member of the population a genuine, known chance of selection, probability sampling, or not, non-probability sampling.
- Note that random and systematic sampling both require a full, accurate sampling frame; if no accurate frame exists, snowball, quota or opportunity sampling may be the only realistic option.
- For evaluation or discuss answers, weigh representativeness against practicality: a probability sample is usually more representative but can be more time-consuming and expensive to arrange.
Worked example
A sociologist wants to survey 100 pupils from a secondary school of 1,000 pupils, using stratified sampling based on year group. Year 7 has 220 pupils, Year 8 has 200, Year 9 has 180, Year 10 has 200 and Year 11 has 200. Calculate how many pupils from each year group should be included in the sample.
- Work out what proportion of the whole school each year group makes up, then apply that proportion to the sample size of 100.
- Year 7: 220 / 1000 x 100 = 22 pupils. Year 8: 200 / 1000 x 100 = 20 pupils. Year 9: 180 / 1000 x 100 = 18 pupils.
- Year 10: 200 / 1000 x 100 = 20 pupils. Year 11: 200 / 1000 x 100 = 20 pupils.
- Check the total sample adds up to 100: 22 + 20 + 18 + 20 + 20 = 100, confirming the stratified sample keeps each year group's true proportion of the school.
Practice questions
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Q1What is a sampling frame?Show answer
Answer: A list of every member of the target population from which a sample can be drawn, for example a school roll or a GP's patient register.
Q2Which sampling technique gives every person in the sampling frame an equal chance of selection using a random number generator?Show answer
Answer: Random sampling.
Q3A researcher selects every 10th name on a sampling frame of 1,000 people to get a sample of 100. Name this technique.Show answer
Answer: Systematic sampling.
Q4Why might a sociologist use snowball sampling to study a group of homeless people?Show answer
Answer: Because there is no accurate sampling frame for this hidden, hard-to-reach population, so existing contacts are used to recruit further participants.
Q5What is the key difference between quota sampling and stratified sampling?Show answer
Answer: Stratified sampling randomly selects people within each subgroup, so it is a probability method; quota sampling lets the researcher pick anyone who fits the required characteristics, so it is a non-probability method.
Q6Give one disadvantage of opportunity sampling.Show answer
Answer: The sample is likely to be unrepresentative, since it only includes people who happen to be available and willing at that particular time and place.
Q7A sociologist stops the first 50 shoppers she meets in a shopping centre. Name this sampling method.Show answer
Answer: Opportunity, or convenience, sampling.
Exam-style questions
Written in the style of a GCSE Sociology exam paper, with a full mark scheme.
Explain two strengths of using stratified sampling to select a research sample.
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A sociologist studying attitudes to marriage stands outside one branch of a supermarket on a Tuesday morning and interviews the first 40 people who agree to speak to her. Evaluate how representative this sample is likely to be of the wider adult population.
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Discuss the strengths and limitations of using random sampling in sociological research.
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