Collecting Data Checkpoint
A free Statistics and Data Analysis lesson from the “Collecting Data” unit, with a worked example and practice problems including step-by-step solutions.
This checkpoint reviews sampling, bias, surveys, observational studies, experiments, control, blinding, simulation, and scope of inference.
What you'll learn
- Review the major skills from this part of the course
- Choose an appropriate statistical method
- Explain results in context
Worked example
Problem. A school wants to learn about homework time for all 9th graders and surveys 90 randomly chosen 9th graders. In this study, what is the sample?
- Worked Example: First identify exactly what the question is asking: A school wants to learn about homework time for all 9th graders and surveys 90 randomly chosen 9th graders. In this study, what is the sample?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- The sample is the group actually measured.
- Here the measured group is the 90 chosen 9th graders.
Answer: the 90 randomly chosen 9th graders
Practice problems
1. Review case A: In a spreadsheet where each row is one order, what is one case?
Choices: one individual row being studied · the average of a column · the whole population only · the answer choice
Show solution
- Checkpoint Review: First identify exactly what the question is asking: In a spreadsheet where each row is one order, what is one case?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- Cases are the individuals or items represented by rows.
- Variables describe something about each case.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: one individual row being studied
2. Review case B: A website posts a poll and counts only people who choose to respond. What bias is most likely?
Choices: random assignment · blocking · a census · voluntary response bias
Show solution
- Checkpoint Review: First identify exactly what the question is asking: A website posts a poll and counts only people who choose to respond. What bias is most likely?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- Voluntary response depends on who chooses to answer.
- People with strong opinions may be overrepresented.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: voluntary response bias
3. Review case C: A health survey may be inaccurate because people hesitate to report habits honestly. What is the concern?
Choices: random assignment · standard error · response bias · cluster sampling
Show solution
- Checkpoint Review: First identify exactly what the question is asking: A health survey may be inaccurate because people hesitate to report habits honestly. What is the concern?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- Response bias happens when answers are not fully honest or accurate.
- Sensitive topics can create this problem.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: response bias
4. Review case D: Patients choose which schedule to follow, then outcomes are compared. Why is this weaker than random assignment?
Choices: the conclusion must be exact · pre-existing differences may explain the result · the study becomes a census · the treatment disappears
Show solution
- Checkpoint Review: First identify exactly what the question is asking: Patients choose which schedule to follow, then outcomes are compared. Why is this weaker than random assignment?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- Self-selected groups can differ before the treatment.
- That makes causal conclusions weaker.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: pre-existing differences may explain the result
5. Review case E: Why does an experiment include a control group?
Choices: to provide a baseline for comparison · to choose the sample randomly · to make a survey question neutral · to compute a histogram
Show solution
- Checkpoint Review: First identify exactly what the question is asking: Why does an experiment include a control group?
- Compare each answer choice with the calculation or rule, and eliminate choices that do not satisfy the condition.
- A control group shows what happens without the new treatment.
- That makes the treatment effect easier to judge.
- Verify the selected choice by checking that it satisfies the original prompt and that the other choices fail the same test.
Answer: to provide a baseline for comparison
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