Sampling Cambridge IGCSE Sociology revision
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In plain words
Nobody can interview a whole country, so sociologists study a slice of it. Everything depends on how the slice is cut. Choose well and a thousand people can speak for millions. Choose badly and they speak only for themselves.
6 things to know
- A sample is a smaller group chosen from the target population. A sampling frame is a list of everyone in the target population, such as a school register, from which the sample is picked.
- Random sampling: every person in the sampling frame has an equal chance of being chosen, for example by a computer picking names. The researcher cannot bias the choice. By chance, the sample may still not be representative.
- Systematic sampling: every nth name is taken from the sampling frame, such as every tenth. It is quick and simple. If the list has a hidden order, the sample may not be representative.
- Stratified sampling: the population is divided into groups, called strata, such as by age or gender. People are then chosen from each group in the same proportions as in the population. It is the most representative. It needs detailed information and takes longer.
- Snowball sampling: the researcher finds one person, who introduces others, who introduce more. It is used for groups that are hard to reach and have no sampling frame, such as gang members. The sample is not representative, because people introduce others like themselves.
- Quota sampling: the researcher is told how many people of each type to find, such as 20 women under 30, and picks whoever is available. It is quick and cheap and needs no sampling frame. The researcher's choice of people can cause bias.
Worked example
A school has 600 girls and 400 boys. A researcher wants a stratified sample of 50 pupils. Calculate how many girls and boys to choose.
- Total pupils = 600 + 400 = 1000.
- Girls are 600 ÷ 1000 = 60% of the school, and boys are 40%.
- Girls in the sample: 60% of 50 = 30. Boys: 40% of 50 = 20.
- Within each group, the 30 and the 20 are chosen at random.
Tips and tricks
- Stratified and quota sampling both use categories. In stratified sampling people are picked at random from a sampling frame. In quota sampling the researcher picks whoever comes along.
- Snowball sampling is the answer when the group is hidden or has no list: drug users, homeless people, victims of a rare crime.
It lands in your notebook with its questions as flashcards.
Sampling: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
In which technique does everyone have an equal chance of being chosen?
Chance alone decides who is picked.
A researcher picks every 20th name on a list. Which technique is this?
A fixed interval makes it systematic.
Which technique is most likely to give a representative sample?
Each group appears in its true proportion.
When is snowball sampling most useful?
One contact leads to the next.
A researcher stops people in a shopping street until she has 25 men and 25 women. What is the main weakness?Stretch
This is quota sampling, and the choice of people is hers.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 10 marks. Write your answers on paper, then check them.
Sampling
Cambridge IGCSE Sociology 0495 · 10 marks · papermunch.org
Name ______________________________ Date ______________
What is meant by the term "sampling frame"?[2]
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A list of all the members of the target population, from which the sample is chosen.
Describe two sampling techniques.[4]
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Any two, each described: random, where everyone has an equal chance of selection; systematic, where every nth name is chosen from a list; stratified, where the population is divided into groups and sampled in proportion; snowball, where one participant introduces others; quota, where the researcher finds a set number of people of each type.
Explain one strength and one limitation of snowball sampling.[4]
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Strength: it gives access to groups that are hard to reach and have no sampling frame, such as gang members. Limitation: participants introduce people similar to themselves, so the sample is unlikely to be representative.
Answers: Sampling
- 1. A list of all the members of the target population, from which the sample is chosen.
- 2. Any two, each described: random, where everyone has an equal chance of selection; systematic, where every nth name is chosen from a list; stratified, where the population is divided into groups and sampled in proportion; snowball, where one participant introduces others; quota, where the researcher finds a set number of people of each type.
- 3. Strength: it gives access to groups that are hard to reach and have no sampling frame, such as gang members. Limitation: participants introduce people similar to themselves, so the sample is unlikely to be representative.