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Chapter 4: Q. 65 (page 264)

Cocoa and blood flow- A study of blood flow involved27healthy people aged18to72.

Each subject consumed a cocoa beverage containing900milligrams of flavanols daily for

5days. Using a finger cuff, blood flow was measured on the first and fifth days of the

study. After5days, researchers measured what they called “significant improvement” in

Blood flow and the function of the cells that line the blood vessels. What a flaw in the

design of this experiment makes it impossible to say if the cocoa really caused the

improved blood flow? Explain your answer.

Short Answer

Expert verified

No flaw in the design of the experiment can make it impossible to say if cocoa cause improvement because no control groups are formed in order for the comparison purposes.

Step by step solution

01

Given information 

We are given a study of the blood flow of healthy people of different age groups, and we have to find the flaw in the design of the experiment that makes it impossible to say if the cocoa really caused the improved blood flow.

02

Explanation

In the given case study, there is no purpose for comparison due to the absence of control groups. It is not given any effects that could affect the blood flow in the human body by cocoa. There is no information if it is a placebo effect, and not even aware of the effect of flavanol on the human body. Hence, there is no flaw in the design of the experiment.

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Most popular questions from this chapter

A local news agency conducted a survey about unemployment by randomly dialing phone

numbers during the work day until it gathered responses from 1000 adults in its state. In

the survey, 19% of those who responded said they were not currently employed. In reality,

only 6% of the adults in the state were not currently employed at the time of the survey.

Which of the following best explains the difference in the two percentages?

a. The difference is due to sampling variability. We shouldn’t expect the results of a

random sample to match the truth about the population every time.

b. The difference is due to response bias. Adults who are employed are likely to lie and

say that they are unemployed.

c. The difference is due to undercoverage bias. The survey included only adults and did

not include teenagers who are eligible to work.

d. The difference is due to nonresponse bias. Adults who are employed are less likely to

be available for the sample than adults who are unemployed.

e. The difference is due to voluntary response. Adults are able to volunteer as a member

of the sample.

A TV station wishes to obtain information on the TV viewing habits in its market area.

The market area contains one city of population 170,000, another city of70,000, and

four towns of about 5000residents each. The station suspects that the viewing habits

may be different in larger and smaller cities and in the rural areas. Which of the

following sampling designs would yield the type of information the station requires?

a. A stratified sample from the cities and towns in the market area

b. A cluster sample using the cities and towns as clusters

c. A convenience sample from the market area

d. A simple random sample from the market area

e. An online poll that invites all people from the cities and towns in the market area to

participate.

One of the better studies of the effect of regular attendance

at religious services gathered data from a random sample of 3617 adults. The researchers then measured lots of variables, not just the explanatory variable (religious activities) and the response variable (length of life). A news article said: “Churchgoers were more likely to be nonsmokers, physically active, and at their right weight. But even after health behaviors were taken into account, those not attending religious services regularly still were significantly more likely to have died.” What conclusion can we draw from this study? Explain your reasoning.

Online reviews Many websites include customer reviews of products, restaurants, hotels,

and so on. The manager of a hotel was upset to see that 26%of reviewers on a travel

website gave the hotel “1star”—the lowest possible rating. Explain how bias in the

sampling method could affect the estimate.

Frozen batteries Will storing batteries in a freezer make them last longer? To find out, a company that produces batteries takes a random sample of 100 AA batteries from its warehouse. The company statistician randomly assigns 50 batteries to be stored in the freezer and the other 50 to be stored at room temperature for 3 years. At the end of that time period, each battery’s charge is tested. Result: Batteries stored in the freezer had a significantly higher average charge. What conclusion can we draw from this study? Explain your reasoning.
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