Sampling

What is a target population?

A large group of individuals that a particular researcher is interested in studying

Why is a sample needed?

Impossible to include all members of a target population

What is a random sample?

Done through obtaining a full list of the population, assigning everyone a number, and then using a lottery method to choose the sample - everyone has an equal chance of being chosen

What is a systematic sample?

Every nth member of the target population is selected from a sampling frame - begun at a random point to reduce bias

What is a stratified sample?

The composition of the sample reflects the proportions of people in subgroups within the target population

What is an opportunity sample?

Researchers obtain sample by selecting anyone who is wiling and available at the time

What is a volunteer sample?

Participants choose to be a part of the sample - eg they may respond to an advert

What are the strengths of a random sample?

Confounding/extraneous variables are equally divided between different groups → potentially unbiased, increasing internal validity

What are the limitations of a random sample?

• Time consuming and difficult to conduct

• Sample may be unrepresentative

• Participants may refuse to take part

What are the strengths of a systemic sample?

Objective - researcher has no influence over who is chosen

What are the limitations of a systemic sample?

• Time consuming

• Participants may refuse to take part

What are the strengths of an opportunity sample?

Less costly and time consuming

What are the limitations of an opportunity sample?

• Unrepresentative of the population → not generalisable

• Potential researcher bias as the researcher has complete control over selection of participants

What are the strengths of volunteer samples?

• Less time-consuming

• Easy

• Participants are more engaged

What are the limitations of a volunteer sample?

Volunteer bias - may attract certain people - not generalisable