Sampling Flashcards
What is meant by the term ‘population’?
The group of individuals the researcher is interested in.
What is meant by the term ‘sample’?
A smaller group taken from the population that the researcher is interested in.
Why is it important that a sample is representative of the target population?
So that generalisations of the findings to the target population can be made.
List the 5 sampling methods.
- Opportunity
- Random
- Stratified
- Systematic
- Volunteer
What is an ‘opportunity sample’?
The researcher recruits those people who are most convenient or most available e.g people walking by on the street, or students at your school.
What is a strength of using an opportunity sample?
It is the easiest method as you are using the first suitable participants that you can find -which takes less time than other methods.
What is a limitation of using an opportunity sample?
It can be biassed - the sample is drawn from a small part of the population and can often vary e.g location depending, time of day.
What is a ‘random sample’? Give examples.
Methods include the lottery method e.g names out of a hat, a random number table, or a random number generator.
What is a strength of using a random sample?
It is unbiased - all members of the target population and therefore have an equal change of selection.
What is a limitation of using a random sample?
The researcher needs to have a list of all members of the population and contact those selected, which takes time.
What is a ‘stratified sample’?
Subgroups (or strata) within a population are identified e.g gender, age groups.
Participants are obtained from each of the strata in proportion to their occurence in the population.
Selection from the strata is done using a random technique.
What is a strength of using a stratified sample?
It is likely to be more representative than other methods as there is a proportional and randomly selected representation of subgroups.
What is a limitation of using a stratified sample?
It can be time consuming to identify subgroups, then randomly select and contact participants.
What is a ‘systematic sample’?
The use of a predetermined system to select participants e.g selecting every 3rd persom the list.
The numberical interval is applied consistently.
What is a strength of using a systematic sample?
It is unbiassed - participants are selected using an objective system.
What is a limitation of using a systematic sample?
It is not truly unbiassed/random unless a number is selected using a random method and the process is started with this person when selected.
What is a ‘volunteer sample’?
Advertisement in a newspaper, online etc - ask those interested in taking part to contact you.
People offer to participate.
What is a strength of using a volunteer sample?
It gives access to a variety of participants which may make the sample more representative and less bias.
What is a limitation of using a volunteer sample?
The sample is still biassed as participants may have more time, more motivation or need the money which is a volunteer bais.
Describe the ‘lottery method’.
- Each persons name is put in a loterry barrel or hat.
- Select the number of names required.
Describe the ‘random number table method’.
- Print a table of random numbers.
- Each member of the population is given a number.
- Place your finger on a random number to select a starting point.
- Select everyone with the numbers in the table from that point.
Describe the ‘random number generator method.’
- Every member of the population is given a number.
- Use a calculator or a computer program to generate a random number between 1 and 100.
What is a sampling bias?
All sampling methods are biased and distorted in some way e.g opportunity sample only represents the people that were available to the researcher at the time.
What is a volunteer bias?
The fact that people volunteer to take part in research are likely to be different to other members of the population and this distorts or biases the data they produce.
