Sampling Methods

WJEC PY3 revision notes on the different types of sampling methods

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Random Sampling

Everyone in the population has an equal chance at being selected. It usually involves the use of a random generator or pulling names out of a hat.


- Can be more representative as each member of the sample as an equal chance of being selected


- The people selected may not want to take part. This can still lead to a biased sample


A university undertook a study of mobile phone use in adolescents. The questionnaire was given to students at a local school by placing all the students names in a container and drawing out 50 names.

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Opportunity Sampling

Selecting people that are available at the time. They have been gathered together for another reason.


- Quicker and more efficient than other methods of sampling


- More likely to have a biased sample


A researcher wished to study memory in children aged between 5 and 11 years. He contacted the headmaster of his local primary school and arranged to test the children in the school.

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Self-Selected (Volunteer) Sampling

Individuals who have chosen to be involved in a study by answering some form of advert.


- Could avoid ethical issues


- Volunteer bias as they tend to be a certain 'type' of people


Milgram (1963) advertised for participants in a local newspaper and by posting adverts to homes in the area near Yale University. The advert said they would be taking part in a memory experiment and that they would be paid $4.50.

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Quota Sampling

Dividing the target population into important subcategories. Selecting Ps from each of thesections using a method such as volunteer or opportunity sampling.


- Useful when time is limited


- May be biased due to opportunity nature


A group of psychology students decided to interview shoppers about their attitudes to dieting. They ensured that they asked people from each age group.

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Stratified Sampling

Dividing the target population into important subcategories. Selecting members in proportion that they occur in the population using random methods.


- Likely to be more representative sample than other methods


- Can be more time consuming to work out the strata required


A polling company employed a panel of people to consult about their opinions on political issues. They identified various subgroups in the population and randomly selected members from each subgroup.

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Systematic Sampling

Using a predetermined system to select participants such as selecting every 10th person from the phone book.


- Less biased as Ps are selected using a objective system


- Lists may not be available of the target population


Buss (1989) posted questionnaires to every 5th house in an area of Venezuela.

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This is really succint  thanks


Very helpful. Thank you.

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