Practice Quiz with Solutions: Chapter 1

Disclaimer: This quiz is representative of the level of difficulty you should expect, but it doesn’t include every single topic from the week’s work. The real quiz may include some other topics and may skip some that are in this practice quiz. (The real quiz also may not word questions in the same way as the practice quiz. You should focus on the concepts, not a particular form of words.)

These solutions show about the same level of work I expect from you, though I add quite a bit of extra commentary. Please see Show Your Work for the what, why, and how.

1(points: 3) Briefly distinguish sampling error from nonsampling error. Which one represents avoidable mistakes? The other type can’t be eliminated, but what can you do to reduce it?

Answer: Sampling error is unavoidable because statistics inevitably vary from one random sample to the next. Nonsampling errors are mistakes in sample technique, such as failure to randomize.

To reduce sampling error, increase your sample size. Nonsampling errors are avoided by proper experimental technique.

2(points: 3) “Of 2500 drivers surveyed, 10% said they got stuck in the snow this week.”
(a) Is this an example of descriptive or inferential statistics?
(b) Is the data type attribute, discrete, or continuous?

Answer: descriptive (summary is stated for data actually gathered); qualitative or attribute (binomial) (“did you get stuck in the snow?”)

3(points: 3) You’re conducting a survey on Tompkins County voters’ willingness to pay for expanded bus routes. You randomly select twenty bus trips on each day one week, and on each selected bus you hand a questionnaire to each person who gets on the bus.
(a) What is the most serious problem with this survey technique?
(b) What vocabulary word have we learned to describe the resulting sample?

Answer: (a) It excludes people who don’t use the bus. This means that people who are dissatisfied with the bus are systematically under-represented. Your survey will show that willingness to pay is higher than it actually is.
(b) biased

Common mistake: I know it sounds like “bias sample”, but the term is “biased sample”.

4(points: 3) “The average American household with children has 2.4 children.”
(a) Is this an example of descriptive or inferential statistics?
(b) Is the data type attribute, discrete, or continuous?

Answer: inferential (you know that not every American household was asked); discrete (“how many children in your household?”)

5(points: 3) You want to test the effectiveness of a new medication for a condition that was previously untreatable. You randomly select thirty doctors from state lists of licensed doctors, and all of them agree to participate.

Each doctor will put up notices in the waiting rooms, and will select the first 30 adult volunteers, assigning the first 15 to the control group and the second 15 to the experimental group. Patients will not be told which group they are in; you supply placebo pills that are identical in appearance to the active medication. Doctors will administer the placebo and medication to the selected groups and report results back to you.

Name three serious errors in this technique. Are these examples of sampling or nonsampling error?

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Practice Quiz with Solutions: Chapter 1 (15 min)