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Chapter 4: Q 3.2. (page 244)

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鈥� babies were born, their birth weights were recorded. The women who received the ultrasounds had heavier babies.

Was the experiment double-blind? Why is this important?

Short Answer

Expert verified

No.

Step by step solution

01

Given information 

Pregnant women participating in the study were randomly assigned to one of two groups.

02

Concept

In a double-blind experiment, neither the subjects nor the people who interact with them and assess the response variable are aware of the treatment they received.

03

Explanation

It wasn't double-blind because neither the subjects nor the researchers knew who had completed the study. Physicians were aware of this. It is critical to eliminate any bias.

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Most popular questions from this chapter

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鈥檚 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 鈥渓ost significantly more weight鈥� 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.

Child care and aggression A study of child care enrolled 1364infants and followed them through

their sixth year in school. Later, the researchers published an article in which they stated that 鈥渢he more time children spent in child care from birth to age four-and-a-half, the more adults tended to rate them, both at age four-and-a-half and at kindergarten, as less likely to get along with others, as more assertive, as disobedient, and as aggressive.鈥�

(a) Is this an observational study or an experiment? Justify your answer.

(b) What are the explanatory and response variables?

(c) Does this study show that child care causes children to be more aggressive? Explain.

Chocolate and happy babies A University of Helsinki (Finland) study wanted to determine if chocolate consumption during pregnancy had an effect on infant temperament at age of 6 months. Researchers began by asking 305 healthy pregnant women to report their chocolate consumption. Six months after birth, the researchers asked mothers to rate their infants鈥� temperament, including smiling, laughter, and fear. The babies born to women who had been eating chocolate daily during pregnancy were found to be more active and 鈥減ositively reactive鈥濃�攁 measure that the investigators said encompasses traits like smiling and laughter.

(a) Was this an observational study or an experiment? Justify your answer.

(b) What are the explanatory and response variables?

(c) Does this study show that eating chocolate regularly during pregnancy helps produce infants with a good temperament? Explain.

Describe how you would carry out the random assignment. Provide enough detail that a classmate could implement your procedure.

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 鈥淒o you plan to diet this year?鈥� More than 30,000 people responded, with 68% saying 鈥淵es.鈥� 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.
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