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- Sampling methods
Sampling methods
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Researchers cannot test everyone, so they study a sample. How the sample is chosen affects whether results can be generalised.
Target population
A sample is the smaller group actually tested.
A representative sample has the same characteristics as the target population, so results can be generalised to it. A biased sample does not.
Four sampling methods
Working out a stratified sample
Girls are 360 out of 600 = 60%. So 60% of 50 = 30 girls.
Boys are 240 out of 600 = 40%. So 40% of 50 = 20 boys.
The sample has the same proportions as the population.
A researcher puts an advert on a noticeboard asking for people to take part in a sleep study. Name the sampling method and give one weakness.
- People choose themselves by responding to the advert: volunteer sampling.
- Volunteers may share characteristics, such as being more interested in sleep, so the sample may be biased.
Answer: Volunteer sampling. Weakness: volunteer bias, so the sample may not represent the target population.
The target population is the group being studied; a sample should be representative. Random sampling gives everyone an equal chance; stratified sampling matches the proportions of sub-groups; volunteer sampling uses people who come forward; opportunity sampling uses whoever is available.
The interactive lesson includes the diagrams for this topic.
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