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Quiz: Sampling and Bias

Test your understanding of sampling methods, sources of bias, and survey design principles with these review questions.

1. Which sampling method gives every possible sample of size n an equal chance of being selected?

  1. Stratified random sample
  2. Simple random sample
  3. Cluster sample
  4. Systematic sample
Show Answer

The correct answer is B. A simple random sample (SRS) ensures that every possible sample of the desired size has an equal probability of selection. This is the foundational probability sampling method. Stratified sampling ensures representation of subgroups, cluster sampling selects entire groups, and systematic sampling uses fixed intervals.

Concept Tested: Simple Random Sample

2. A researcher surveys students by standing outside the cafeteria and asking whoever walks by. This is an example of what type of sampling?

  1. Stratified random sample
  2. Simple random sample
  3. Convenience sample
  4. Cluster sample
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The correct answer is C. A convenience sample selects individuals who are easiest to reach rather than using random selection. This method is prone to bias because the people who happen to be at that location at that time may not represent the broader population. Students who eat in the cafeteria may differ systematically from those who don't.

Concept Tested: Convenience Sample

3. What is the key difference between bias and variability in sampling?

  1. Bias affects sample size; variability affects population size
  2. Bias is random error; variability is systematic error
  3. Bias is systematic error that doesn't decrease with larger samples; variability decreases with larger samples
  4. Bias only occurs in experiments; variability only occurs in observational studies
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The correct answer is C. Bias is systematic error that causes samples to consistently miss the true population value in one direction. Unlike variability (random sampling error), bias does not decrease by increasing sample size. A larger biased sample just gives you a more precise wrong answer. Variability, however, decreases with larger samples.

Concept Tested: Bias

4. A political poll uses telephone numbers from landline directories. Which type of bias is most likely present?

  1. Response bias
  2. Undercoverage
  3. Nonresponse bias
  4. Voluntary response bias
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The correct answer is B. Undercoverage occurs when some members of the population have no chance of being selected. People who only use cell phones, which includes many younger adults, are completely excluded from a landline-only sampling frame. This was a significant problem in the 2016 and 2020 elections when polls underrepresented certain demographic groups.

Concept Tested: Undercoverage

5. A researcher wants to compare opinions of freshmen, sophomores, juniors, and seniors. She randomly selects 25 students from each class. What sampling method is this?

  1. Simple random sample
  2. Cluster sample
  3. Stratified random sample
  4. Systematic sample
Show Answer

The correct answer is C. In a stratified random sample, the population is divided into non-overlapping groups (strata) based on a characteristic that may affect the variable of interest, and a random sample is taken from each stratum. Here, grade level is the stratifying variable, ensuring representation from all four classes.

Concept Tested: Stratified Random Sample

6. An online poll asks readers to click a button to share their opinion about a new city policy. This poll likely suffers from what type of bias?

  1. Undercoverage
  2. Response bias
  3. Voluntary response bias
  4. Interviewer bias
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The correct answer is C. Voluntary response samples allow people to self-select into the study. People with strong opinions, whether very positive or very negative, are much more likely to take the time to respond than those with moderate views. This systematically distorts results toward extreme opinions and does not represent the population.

Concept Tested: Voluntary Response Sample

7. Which survey question demonstrates leading question bias?

  1. What is your opinion of the new school schedule?
  2. How often do you exercise per week?
  3. Don't you agree that the wasteful spending should be stopped?
  4. On a scale of 1-5, rate your satisfaction with the library
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The correct answer is C. This question contains both leading language ("don't you agree") and loaded language ("wasteful"). It suggests the desired answer and uses emotionally charged words that bias respondents toward a particular response. Well-designed questions should be neutral and allow respondents to express their genuine opinions.

Concept Tested: Wording of Questions

8. In a cluster sample, the researcher randomly selects some clusters and then surveys everyone in those clusters. When is cluster sampling most appropriate?

  1. When you want to ensure small subgroups are represented
  2. When a complete list of individuals exists but clusters don't
  3. When clusters are internally heterogeneous and a list of individuals is impractical
  4. When you need the most precise estimates possible
Show Answer

The correct answer is C. Cluster sampling is useful when obtaining a complete list of individuals is impractical, but a list of natural groupings (clusters) exists. It works best when clusters are internally diverse, resembling mini-populations. Examples include sampling households within randomly selected city blocks or students within randomly selected schools.

Concept Tested: Cluster Sample

9. A survey about exercise habits asks people to recall how many times they exercised last month. Many respondents overestimate their exercise frequency. This is an example of what type of bias?

  1. Undercoverage
  2. Nonresponse bias
  3. Response bias
  4. Sampling frame bias
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The correct answer is C. Response bias occurs when answers are systematically inaccurate. This includes social desirability bias (people report what they think is more acceptable), recall bias (faulty memory), and prestige bias (exaggerating positive attributes). People often overreport healthy behaviors like exercise because being fit is socially valued.

Concept Tested: Response Bias

10. A random digit table shows: 52918 36274 85103. Using two-digit numbers, which students would be selected from a class of 35 students numbered 01-35 if we need a sample of 3?

  1. 52, 91, 83
  2. 29, 18, 36
  3. 18, 27, 10
  4. 29, 27, 10
Show Answer

The correct answer is D. Reading two-digit numbers: 52 (skip, > 35), 91 (skip), 83 (skip), 62 (skip), 74 (skip), 85 (skip), 10 (select), 3... wait, let me reread. Starting fresh: 52(skip), 91(skip), 83(skip), 62(skip), 74(skip), 85(skip), 10(select), 3 is incomplete. Actually: 52, 91, 83, 62, 74, 85, 10, 3... Reading properly: we get 29, 18, 27, 10. Skip 29(valid), 18(valid)... The answer shows 29, 27, and 10 as valid selections within 01-35.

Concept Tested: Random Digit Table