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Chapter 4: Q T4.14. (page 276)

Many people start their day with a jolt of caffeine from coffee or a soft drink. Most experts agree that people who take in large amounts of caffeine each day may suffer from physical withdrawal symptoms if they stop ingesting

their usual amounts of caffeine. Researchers recruited 11 volunteers who were caffeine-dependent and who were willing to take part in a caffeine withdrawal experiment. The experiment was conducted on two 2-day periods that

occurred one week apart. During one of the 2-day periods, each subject was given a capsule containing the amount of caffeine normally ingested by that subject in one day. During the other study period, the subjects were given placebos. The order in which each subject received the two types of capsules was randomized. The subjects’ diets were restricted during each of the study periods. At the end of each 2-day study period, subjects were evaluated using a tapping task in which they were instructed to press a button 200 times as fast as they could.

(a) How and why was blocking used in the design of this experiment?

(b) Why did researchers randomize the order in which subjects received the two treatments?

(c) Could this experiment have been carried out in a double-blind manner? Explain.

Short Answer

Expert verified

Part (a) Blocking is being used by providing the treatments to the subjects.

Part (b) The orders have been shuffled.

Part (c) It's possible that the survey will be double-blind.

Step by step solution

01

Part (a) Step 1: Given information

Many people are starting their day by having either caffeine or a cold drink.

02

Part (a) Step 2: Concept

The treatments are randomly assigned to all of the experimental units in a completely randomized design.

03

Part (a) Step 3: Explanation

Many people begin their day with either caffeine or a cool beverage. Researchers agree that those who use significant amounts of caffeine may experience withdrawal symptoms. Various volunteers have been recruited as a result of these efforts. Blocking is the technique of grouping the experimental units into groups that are comparable. Every brick represents one of the persons who will receive therapy. By administering therapies to the subjects, blocking is employed.

04

Part (b) Step 1: Explanation

Because there may be fluctuations in the outcomes and the correct or actual results may not be achieved, orders have been randomized here.

05

Part (c) Step 1: Explanation

If both the researchers and the subjects are unaware of the treatments they are receiving, the survey could be double blind.

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Most popular questions from this chapter

Acupuncture and pregnancy A study sought to determine whether the ancient Chinese art of acupuncture could help infertile women become pregnant.41 One hundred sixty healthy women undergoing treatment with artificial insemination were recruited for the study. Half of the subjects were randomly assigned to receive acupuncture treatment 25minutes before embryo transfer and again 25

minutes after the transfer. The remaining 80subjects were instructed to lie still for 25minutes after the embryo transfer.

Results: In the acupuncture group, 34women became pregnant. In the control group, 21women became pregnant.

(a) Describe how the three principles of experimental design were addressed in this study.

(b) The difference in the percent of women who became pregnant in the two groups is statistically significant. Explain what this means to someone who

knows little statistics.

(c) Explain why the placebo effect prevents us from concluding that acupuncture caused the difference in pregnancy rates.

Who goes to the convention? A club has 30 student members and 10 faculty members. The students are

The club can send 4 students and 2 faculty members to a convention. It decides to choose those who will go by random selection. How will you label the two strata? Use Table D, beginning at line 123 to choose a stratified random sample of 4 students and 2 faculty members.

Do reducing diets work? Dr. Linda Stern and her colleagues recruited 132obese adults at the Philadelphia Veterans Affairs Medical Center in Pennsylvania. Half of the participants were randomly assigned to a low-carbohydrate diet and the other half were assigned to a low-fat diet. Researchers measured each participant’s change in weight and cholesterol level after six months and again after one year. Subjects in the low-carb diet group lost significantly more weight than subjects in the low-fat diet group during the first six months of the study. At the end of a year, however, the average weight loss for subjects in the two groups was not significantly different.

(a) Why did researchers randomly assign the subjects to the diet treatments?

(b) Explain to someone who knows little statistics what “lost significantly more weight” means.

(c) The subjects in the low-carb diet group lost an aver-age of 5.1kg in a year. The subjects in the low-fat diet group lost an average of 3.1kg. Explain how this infor-

mation could be consistent with the fact that weight loss in the two groups was not significantly different.

Each of the following is a source of error in a sample survey. Label each as sampling error or non sampling error, and explain your answers.

(a) The telephone directory is used as a sampling frame.

(b) The person cannot be contacted in five calls.

(c) Interviewers choose people walking by on the sidewalk to interview.

2. A survey paid for by makers of disposable diapers found that 84% of the sample opposed banning disposable diapers. Here is the actual question:

Reducing unemployment Will cash bonuses speed the return to work of unemployed people? A state department of labor notes that last year 68%of people who filed claims for unemployment insurance found a new job within 15weeks. As an experiment, this year the state offers $500to people filing unemployment claims if they find a job within 15weeks. The percent who do so increases to 77%. What flaw in the design of this experiment makes it impossible to say whether the bonus really caused the increase? Explain.
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