What is opportunity sampling?
Taking people who are simply most available
I.e. The ones who are nearest/easiest to obtain
What are strengths of opportunity sampling?
- quick and convenient
- most popular sampling method
What are the weaknesses of opportunity sampling?
- sample is unrepresentative of target population as it’s drawn from a specific area
- meaning findings cannot be generalised
How would you do opportunity sampling?
Ask people nearby
E.g. Ask the students in your class or people nearby in a shopping centre
What is random sampling ?
Every person in target population has an equal chance of being selected by using a statistical method
How would you do random sampling ?
By lottery method .
All members of the target population are given a number and placed in a hat
What are the strengths of random sampling ?
- free from researcher bias. Researcher had no influence over who is selected
What are the weakness of random sampling?
- representation not guaranteed
- limits ability to generalise
- time consuming
What is volunteer (self-selected) sampling?
Participants respond to an advertisement to take part in a study
How do you do volunteering sampling ?
Advertise
What are the strengths of volunteer sampling?
- Participants are willing to do the research
- quick and easy
What are the weaknesses of volunteer sampling ?
- generalisation limited due to volunteer bias
- participants may share certain traits e.g. Keen and curious
- people CBA to turn up, and they differ from non-volunteers
What is systematic sampling?
Participants are selected using a set ‘pattern’ (sampling frame)
How do you do systematic sampling?
Every nth person is selected from a database of target population
What are the strengths of systematic sampling?
- unbiased (little chance of it)
- convenient & simple
What are the disadvantages of systematic sampling ?
- sampling error
- complete database of population is required (time and effort)
What is stratified sampling?
Participants are selected according to their frequency in the target population
How do you do stratified sampling?
Subgroups are identified (or she, gender) the relative percentages of the subgroups in the population are reflected in the sample
What are the strengths of stratified sampling ?
- reduces selection bias
- characteristics of the target pop are representative
- generalisability more likely than other methods
What are disadvantages of stratified sampling?
Subgroups cannot reflect all ways in which people are different
- complete representation is not possible
- each participant must be identified (time and effort)
What is selection bias?
Researcher may avoid certain people or places due to uncertainty or uncomfortablity
What is the target population
Refers to the entire group of individuals to which researchers are interested in generalising
I.e. Group of doctors, teachers
What is a sample?
A group of participants extracted from target population, should be representative
