Chapter 7: Sampling & External Validity

What is a population of interest vs a sample from the population?

• Population = all members of the group we want to study

• Sample = a subset of the members within our group of interest

What is sampling?

The process by which the researcher recruits a sample from a population

What is probability vs non-probability sampling?

• Probability - every member of the population has an equal chance of being selected (employs random sampling)

• Non-probability - results in a biased sample

What are the different types of probability sampling? (5)

• Simple random

• Cluster

• Multistage

• Stratified

• Systematic

What is simple random sampling?

Sample is chosen at random; participants have an equal chance of being selected

What is cluster sampling?

Clusters (groups) of participants are randomly selected, followed by data collection from everyone within each cluster

What is multistage sampling?

Random sample of clusters followed by random sample of people within selected clusters

What is stratified sampling?

Researcher identifies particular demographic (strata), then randomly selects individuals within each category

What is systematic sampling?

Researcher randomly chooses N, and counts off every Nth member

What are different types of non-probability sampling? (4)

• Convenience

• Purposive

  • Snowball

• Quota

What is convenience sampling?

Sampling those who are accessible and readily available

What is purposive sampling?

Only certain kinds of people are included in the sample (snowball)

What is snowball sampling?

Participants are asked to recommend acquaintances for the study

What is quota sampling?

A researcher identifies subsets of the population, sets a target number for each category, and nonrandomly selects individuals within each category until quotas are filled

What is a WEIRD sample?

• Western

• Educated

• Industrial

• Rich

• Democratic

What is ecological validity?

The extent to which the tasks and manipulations of a study are similar to real-world contexts