AP Statistics Unit 3: Collecting Data

Unit 3 covers data collection: sampling methods, experimental design, bias and randomisation. It is short on computation and heavy on judgement — most questions ask what a design does or does not allow you to conclude.

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190 questions6 CED topics100% with a figure
How this unit behaves

What 190 questions on it look like

100% of the questions come with a figure — a graph, diagram or data display. Reading the figure correctly is most of the work before any content knowledge applies.

Selecting an Experimental Design52
Introduction to Experimental Design51
Potential Problems with Sampling31
Random Sampling and Data Collection30
Inference and Experiments25
Introduction to Planning a Study1

Questions per CED topic.

From the bank

Three real collecting data questions

Drawn from the practice pool, not from the mock papers.

Random Sampling and Data Collection · Selecting Statistical Methods · with figure

The after-school robotics league alpha cycle has lists of teams within each mentor. A planner wants each mentor represented when estimating battery swap completion. Which design is most appropriate?

  1. AChoose one mentor and survey everyone in it.
  2. BA large convenience sample removes selection bias because increasing sample size alone makes the sample representative.
  3. CInvite the first 90 teams who notice the prototype cart.
  4. DLet staff pick teams they think are typical.
  5. EStratify by mentor, then randomly select teams within each stratum.correct
Why E is correct

Stratified random sampling is best because the planner first separates teams by mentor and randomly samples within every group, ensuring representation while preserving randomness.

Stratified random sampling for after-school robotics league alpha cycle: the important cue is the after-school robotics league alpha cycle setting. Match the method to the way the data are collected or the statistic is computed, then state the conclusion in the language of the stem.

Common mistakes. Stratified random sampling for after-school robotics league alpha cycle: Do not replace stratified sampling with a convenience list.

Potential Problems with Sampling · Statistical Argumentation · with figure

A river cleanup coalition alpha cycle posts an online link on a bulletin board marked collection jar. Only volunteers who feel strongly about microplastic count respond. Which concern is most direct?

  1. AVoluntary response bias; the responding volunteers may not represent the whole group.correct
  2. BA large convenience sample removes selection bias because increasing sample size alone makes the sample representative.
  3. CThe response variable is categorical only.
  4. DThe sample size is automatically too small.
  5. EA matched-pairs design is missing.
Why A is correct

This is voluntary response bias because volunteers choose whether to respond, and those with strong opinions about microplastic count may be overrepresented.

Voluntary response bias in river cleanup coalition alpha cycle: the important cue is the river cleanup coalition alpha cycle setting. Match the method to the way the data are collected or the statistic is computed, then state the conclusion in the language of the stem.

Common mistakes. Voluntary response bias in river cleanup coalition alpha cycle: Do not call a self-selected survey a random sample.

Introduction to Experimental Design · Statistical Argumentation · with figure

For the mobile dental clinic alpha cycle, researchers randomly assign comparable patients to receive either a new reminder card reminder or the usual reminder, then compare appointment follow-up. What feature supports a cause-and-effect conclusion?

  1. AA large voluntary response survey about appointment follow-up.
  2. BRandom assignment of patients to reminder conditions.correct
  3. CReporting only the group with the better appointment follow-up.
  4. DUse volunteers.
  5. EUsing only one neighborhood to make data collection easier.
Why B is correct

Random assignment to the reminder treatments helps balance other variables between groups, so differences in appointment follow-up can more plausibly be attributed to the reminder condition.

Random assignment in an experiment for mobile dental clinic alpha cycle: the important cue is the mobile dental clinic alpha cycle setting. Match the method to the way the data are collected or the statistic is computed, then state the conclusion in the language of the stem.

Common mistakes. Random assignment in an experiment for mobile dental clinic alpha cycle: Random sampling and random assignment answer different questions.

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FAQ

Collecting Data questions

When can I generalise to a population?

Only when the sample was randomly selected from it. Random assignment supports causation; random selection supports generalisation.

What is blocking?

Grouping similar units before randomising within each group, so a known source of variability does not obscure the treatment effect.
Last reviewed 2026-08-28. Unit and topic names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.
Topic by topic

Worked questions by topic

5 of this unit’s topics have enough practice questions for a page of their own.

Random Sampling and Data Collection30 questionsPotential Problems with Sampling31 questionsIntroduction to Experimental Design51 questionsSelecting an Experimental Design52 questionsInference and Experiments25 questions
Same course
Unit 1: Exploring One-Variable Data460 questionsUnit 2: Exploring Two-Variable Data295 questionsUnit 4: Probability, Random Variables, and Probability Distributions100 questionsUnit 5: Sampling Distributions70 questionsUnit 6: Inference for Categorical Data: Proportions107 questionsUnit 7: Inference for Quantitative Data: Means63 questionsUnit 9: Inference for Quantitative Data: Slopes133 questions

Practise collecting data until the reasoning is automatic.

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