Sampling

• People who take part in psychology research are called participants.
• Before selecting a sample, the target population needs to be identified; this is the group of people whose behaviour the experimenter wants to investigate.
• Sampling method/technique - because it is not possible to test everyone
• Actual sample
• Representative sample - A sample that represent the population

There are several different types of sampling, find out about the following types and give and example of when they may be useful : Opportunity, Self-Selected or Volunteer, Stratified, Random and Snowball

Opportunity - A sample made up of anybody who is suitable and available.
E.g: Most researchers are based in university psychology departments - samples are usually composed of undergraduate students.
Problem: They are hardly representative of the population as a whole - lacking external validity + Ethical issues

Self-Selected or Volunteer - A sample drawn from people who volunteer to take part in the research.
E.g: Questionnaires / Newspapers or magazines
Problem: The participants are self-selected - they may differ in important respects from those who did not volunteer + not representative of the population

Stratified - A sample which reflects the proportion of certain characteristics in the target population.
Problem: Your various subsets might be unequal in size (e.g. male/female, smoker/non-smoker, etc)

Random - A sample which is randomly selected from the target population.
Problem: Can we meaningfully generalise data from a small sample, even if it is a random sample? Very impractical.

Snowball - A sample drawn from introductions provided by members of the target population
Problem: It is impossible to determine the possible sampling error and make statistical inferences from the sample to the population. As such, snowball samples should not be considerate to be representative of the population being studied.