Loading…
Identify sources of bias in sampling and surveys including voluntary response and convenience sampling.
Learn step-by-step with practice exercises built right in.
Bias occurs when the method of collecting data systematically favors certain outcomes. A biased study does not accurately represent the population.
People choose whether to participate. Those with strong opinions are more likely to respond.
Example: An online poll asking "Do you support this policy?" — people who feel strongly will disproportionately respond.
The researcher selects individuals who are easy to reach.
Example: Surveying students in the cafeteria to represent all students.
Some groups in the population are left out of the sampling frame.
Example: A phone survey that only calls landlines misses people who only use cell phones.
Selected individuals cannot be contacted or refuse to participate.
No example problems available yet.
Avoid these 3 frequent errors
Review key concepts with our flashcard system
Explore more AP Statistics topics
Example: A mailed survey with only a 20% return rate — the 80% who didn't respond may differ systematically from those who did.
The way a question is phrased can influence the answer.
Example: "Do you agree that the government should protect endangered species?" (leading question)
Respondents give answers they think are socially acceptable rather than truthful.
Example: "How often do you exercise?" — people tend to overreport.
The presence or characteristics of the interviewer influences responses.
| Type of Bias | Problem | Solution |
|---|---|---|
| Voluntary response | Strong opinions overrepresented | Use random sampling |
| Convenience | Not representative | Use random sampling |
| Undercoverage | Some groups excluded | Improve sampling frame |
| Nonresponse | Non-responders differ | Follow up, incentives |
| Question wording | Leading questions | Use neutral wording |
| Social desirability | Dishonest answers | Anonymous surveys |
AP Tip: When identifying bias, (1) name the type of bias, (2) explain the direction of bias (overestimates or underestimates), and (3) explain why in context.