Sampling Methods

Volunteer

• 
• Caption: Example of a Volunteer method (Milgram's advertisement)
• Participants offer to take part in research after seeing advertisements.
• Advantage
• No researcher bias - sample is more likely to represent the population.
• Disadvantage
• Volunteer bias - participants are likely to be helpful, in need of possible money offered and have free time.

Opportunity

• Every member of the population has an equal chance of being selected.
• Advantages
• Quick and convenient
• More representative as it is a random selection.
• Disadvantage
• Unrepresentative - Could still select participants that are really similar.
• Possible research bias.
• 
• Caption: Asking people is an example of Opportunity Sampling.

Random

• Researcher selects anyone who is available and willing to take part in the study.
• Advantage
• Quick and convenient
• Disadvantage
• Biased - sample is from a small part of the population so is not representative of the population and cannot be generalised.
• 
• Caption: Example of random sampling.