Math 183 Sampling

Self-selection bias

Occurs when individuals who volunteer to participate differ from those who do not, leading to an unrepresentative sample.

Non-response bias

Occurs when individuals selected for the survey do not respond, and those who don’t respond differ systematically from those who do.

Response bias

Occurs when the way a question is asked or the environment of the survey influences how participants respond.

Quota sampling

A non-random sampling plan where interviewers must fill quotas for certain groups but select specific individuals at their discretion.

Sampling volunteers

A sampling plan where people are asked to volunteer; only those who volunteer are included in the sample.

Convenience sampling

A sampling plan that selects individuals who are easiest to reach, not randomly chosen from the whole population.

Simple random sampling

A sampling method in which every member of the population has an equal chance of being selected.

Systematic sampling

A sampling method in which every nth individual is chosen from a list or sequence.

Stratified sampling

The population is divided into subgroups (strata) based on shared characteristics, and random samples are taken from each subgroup.

Cluster sampling

The population is divided into groups (clusters), some clusters are randomly chosen, and all (or some) individuals within those clusters are surveyed.

Multistage sampling

A complex form of cluster sampling where random sampling occurs at multiple stages, often combining different sampling methods (e.g., clusters, then random sampling within clusters).

A researcher surveys every fifth person who enters the library.

Systematic sampling

A political party sends surveys only to its registered members and uses the responses to estimate opinions of all voters.

Self-selection bias

A professor stands outside the campus cafeteria and asks the first 20 students who walk by to complete a survey.

Convenience sampling

A health study mails questionnaires to a random sample of city residents, but only 30% return the survey.

Non-response bias

An online poll is posted on a news website and anyone who visits can participate.

Sampling volunteers

A researcher divides a city into neighborhoods by income level, then randomly selects people from each neighborhood for a survey.

Stratified sampling

A company assigns interviewers to survey exactly 10 people from each age group, allowing the interviewer to choose whomever they want.

Quota sampling

A school randomly selects three classrooms and surveys every student in those rooms.

Cluster sampling

A social media influencer asks their followers to fill out a survey about shopping habits.

Self-selection bias

A national survey randomly selects several regions, then randomly selects households within each region, then interviews one adult from each selected household.

Multistage sampling

A survey asks sensitive questions about illegal drug use, and some respondents give false answers.

Response bias

A sports study asks for volunteers at a marathon finish line, so the results mostly represent experienced runners.

Sampling volunteers