Each member of the target population has an equal chance of being selected.
The research writes all the names of the members of the target population on pieces of paper that are the same size. They are folded in half and placed in a hat. The researcher picks out how many needed for the sample size without looking, to prevent bias, and they become the sample.
- Provides the best chance of an unbiased sample - high population validity.
- Writing out all the names of the target population can be expensive and time-consuming.
- Can still be unrepresentative (EG: all girls in one group, all boys in another or if people refuse to take part) so a chance of bias.
Consists of those people available to the researcher.
The researcher simply approaches members of the target population and asks if they would like to take part in the study. If they agree then they become part of the sample.
- Convenient and economical.
- Can be unrepresentative and biased.
- People may feel obliged to take part even if they don't want to.
Participants self-select to take part.
The research would put an advert up and those people who respond would become part of the sample.
- Can be unrepresentative as particular type of people are more likely to volunteer (highly motivated with a lot of time on their hands) so a good chance of bias.