Sampling Flashcards
Opportunity sampling
- a sample of participants produced by selecting people who are most easily available at the time of the study
Advantages of opportunity sampling
- easy method
- use the first suitable participants
- takes less time to locate the sample
Disadvantage of opportunity
- can be biased because the sample is drawn from a small part of the target population
e.g if selecting people walking around the centre at 9am then they are less likely to be professionals because professionals would be at work
Random sampling
- sample of participants produced using a random technique so that every member of the target population being tested has an equal chance
- would do this by using the lottery method which is essentially drawing names out of a hat
To do this obtain a list of people in your target population, put their names in a hat and select the number of names required
Advantages of random sampling
- unbiased as all members of the target population have an equal chance at selectiom
Disadvantages of random sampling
- time consuming as you need a list of all the target population then you would need to contact those who have been selected
What is a target population?
- a group of individuals the researcher is interested in studying e.g babies in the western world, people in the UK
- the researcher intends to make a statement about these groups of people
Snowball sample
The referral from initial participants to generate additional participants
- recruit further participants from among people they know
Advantages of snowball
Enables researchers to locate groups of people who are difficult to access e.g drug lords
Disadvantages of snowball
- not likely to be a good cross section of the target population as it is normally friends of friends
Self selected sampling
- sample of participants that relies solely on volunteers to make up the sample
- can be done by advertising in a newspaper or noticeboard or on the internet
Advantages of self selected
- gives access to a variety of participants which makes the sample more representative and less biased
Disadvantages of self selected
- sample is biased in other ways because participants are more likely to be highly motivated to being helpful - results in volunteer bias
Stratified and quota sampling
Stratified sampling - a sample obtained by selecting every nth participant and this can be random and every nth person after that is who you select
Quota sampling - similar to stratified sampling except participants are not selected from a strata using a random sampling technique
- subgroups (strata) within a target population are identified e.g boys and girls and they are obtained from each of the strata in proportion to their occurrence in the target population - done using random techniques and quota is done using non random techniques
Advantages to stratified and quota
likely to be more representative than other methods because there is a proportional representation of subgroups
Disadvantages to stratified and quota
- very time consuming to identify subgroups and then select participants and contact them
Systematic sampling
A sample obtained by selecting every nth person - this can be a random sample if the first person is selected using a random method and then you select every nth person after that
- use a predetermined system to select participants e.g every 6th, 14th, 20th from a phonebook and the numerical interval is applied consistently
Advantages of systematic sampling
Unbiased participants are selected using a subjective system
Disadvantages of systematic sampling
Not truly unbiased unless you select a number using a random method and start with said person and then select every nth person
Sampling frame
The source material from which a sample is drawn
Bias
A systematic distortion
Sampling
The selection of participants from the sampling frame with the aim of producing a representative frame with the aim of producing a representative selection of people from that group
