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The Practice of Statistics for AP

David Moore,Daren Starnes,Dan Yates

$Math Studyset Vaia Explanations$ Math

4th Edition · 809 pages

ISBN: 9781319113339

Chapter 4: Q 1.1. (page 233)

Does reducing screen brightness increase battery life in laptop computers? To find out, researchers obtained $30$ new laptops of the same brand. They chose $15$ of the computers at random and adjusted their screens to the brightest setting. The other $15$ laptop screens were left at the default setting—moderate brightness. Researchers then measured how long each machine’s battery lasted.
Was this an observational study or an experiment? Justify your answer.

Short Answer

Expert verified

Experimental Study.

Step by step solution

01

Given information

They randomly selected $15$ laptops and set their screens to the brightest setting. The default setting for the other $15$ laptop screens was moderate brightness.

02

Concept

Observational research looks at people and assesses factors of interest without trying to affect their responses.

Individuals are purposely subjected to a treatment in order to measure their responses in an experiment.

03

Explanation

This is an experimental study in which the evaluation group and the control group are both classes, each with the appropriate variable adjustments to meet the criteria in a controlled setting.

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Most popular questions from this chapter

The Web portal AOL places opinion poll questions next to many of its news stories. Simply click your response to join the sample. One of the questions

in January $2008$ was “Do you plan to diet this year?” More than $30, 000$ people responded, with $68 %$ saying “Yes.” You can conclude that

(a) about $68 %$ of Americans planned to diet in $2008$

(b) the poll used a convenience sample, so the results tell us little about the population of all adults.

(c) the poll uses voluntary response, so the results tell us little about the population of all adults.

(d) the sample is too small to draw any conclusion.

(e) None of these.

Students as customers A high school student the newspaper plans to survey local businesses about the importance of students as customers. From telephone book listings, the newspaper staff chooses $150$ businesses

at random. Of these, $73$ return the questionnaire mailed by the staff. Identify the population and the sample.

Sampling by accountants Accountants often use stratified samples during audits to verify a company’s records of such things as accounts receivable. The

stratification is based on the dollar amount of the item and often includes $100 %$ sampling of the largest items. One company reports $5000$ accounts receivable. Of these, $100$ are in amounts over $\(50, 000; 500$ are in amounts between $\) 1000 a n d \(50, 000;$ and the remaining $4400$ are in amounts under $\) 1000$ Using these groups as strata, you decide to verify all the largest accounts and to sample $5 %$ of the midsize accounts and $1 %$ of the small accounts. How would you label the two strata from which you will sample? Use Table D, starting at line $115$ to select only the first $3$ accounts from each of these strata.

Got deodorant? A group of students wants to perform an experiment to determine whether Brand A or Brand B deodorant lasts longer. One group member

suggests the following design: Recruit $40$ student volunteers— $20$ male and $20$ female. Separate by gender, since male and female bodies might respond

differently to deodorant. Give all the males Brand A deodorant and all the females Brand B. Have each student rate how well the deodorant is still working at the end of the school day on a 0 to 10 scale. Then compare ratings for the two treatments.

(a) Identify any flaws you see in the proposed design for this experiment.

(b) Describe how you would design the experiment. Explain how your design addresses each of the problems you identified in (a).

In an interesting experiment, researchers examined the effect of ultrasound on birth weight. Pregnant women participating in the study were randomly assigned to one of two groups. The first group of women received an ultrasound; the second group did not. When the subjects’ babies were born, their birth weights were recorded. The women who received the ultrasounds had heavier babies.

Based on your answers to Questions $1$ and $2$ , describe an improved design for this experiment

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