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Chapter 4: Q 10. (page 226)

A sampling at the mall You have probably seen the mall interviewer, approaching people passing by with a clipboard in hand. Explain why even a large sample of mall shoppers would not provide a trustworthy estimate of the current unemployment rate.

Short Answer

Expert verified

Because the unemployed have more time off than those who reside in the mall, the unemployment rate will most likely be greater.

Step by step solution

01

Given information

Given the sample size, n

Because the provincial health-care system is meeting its objectives, the Ministry of Health conducted the Ontario Health Survey.

02

Concept

A simple random sample (SRS) of size n is made up of n people chosen from the population with an equal chance of being the sample that is actually chosen.

03

Explanation

A big sample of mall customers would not produce a reliable estimate of the current unemployment rate because it is easy to find a large number of people in a mall, hence this is a convenience sample. Because the unemployed have more time to spend at the mall than those who are employed, a large sample of mall visitors would not yield a reliable estimate of the present unemployment rate.

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Most popular questions from this chapter

Baseball tickets Suppose you want to know the average amount of money spent by the fans attending opening day for the Cleveland Indians baseball season. You get permission from the team’s management to conduct a survey at the stadium, but they will not allow you to bother the fans in the club seating or box seats (the most expensive seating). Using a computer,

you randomly select 500 seats from the rest of the stadium. During the game, you ask the fans in those seats how much they spent that day.

(a) Provide a reason why this survey might yield a biased result.

(b) Explain whether the reason you provided in (a) is a sampling error or a non sampling error.

Killing weeds A biologist would like to determine which of two brands of weed killer is less likely to harm the plants in a garden at the university. Before spraying near the plants, the biologist decides to conduct an experiment using 24 individual plants. Which of the following two plans for randomly assigning the treatments should the biologist use? Why?

Plan A: Choose the 12healthiest-looking plants.

Apply Brand X weed killer to all 12of those plants.

Apply Brand Y weed killer to the remaining 12plants.

Plan B: Choose 12of the 24plants at random. Apply

Brand X weed killer to those 12plants and Brand Y

weed killer to the remaining 12plants.

Treating prostate disease A large study used records from Canada’s national health care system to compare the effectiveness of two ways to treat prostate

disease. The two treatments are traditional surgery and a new method that does not require surgery. The records described many patients whose doctors had

chosen each method. The study found that patients treated by the new method were significantly more likely to die within eight years.

(a) Further study of the data showed that this conclusion was wrong. The extra deaths among patients who got the new method could be explained by lurking variables. What lurking variables might be confounded with a doctor’s choice of surgical or nonsurgical treatment?

(b) You have 300prostate patients who are willing to serve as subjects in an experiment to compare the two methods. Write a few sentences describing how you would design this experiment.

A simple random sample of 1200 adult Americans is selected, and each person is asked the following question: “In light of the huge national deficit, should the government at this time spend additional money to establish a national system of health insurance?” Only 39% of those responding answered “Yes.” This survey

(a) is reasonably accurate since it used a large simple random sample.

(b) needs to be larger since only about 24 people were drawn from each state.

(c) probably understates the percent of people who favor a system of national health insurance.

(d) is very inaccurate but neither understates nor overstates the percent of people who favor a system of national health insurance. Since simple random sampling was used, it is unbiased.

(e) probably overstates the percent of people who favor a system of national health insurance.

Wake-up call Do people naturally wake up earlier when they set an alarm before going to sleep? Justin decides to conduct his own experiment to find out. On Friday and Saturday nights, he doesn’t set the alarm before going to bed. On Monday and Tuesday, he sets the alarm for 7a.m. Justin records the time when he wakes up each day and then compares his average wake-up time with and without the alarm.

(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).
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