Question

Do diets work? Dr. Linda Stern and her colleagues recruited 132 obese adults at the

Philadelphia Veterans Affairs Medical Center in Pennsylvania. Half the participants

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were randomly assigned to a low-carbohydrate diet and the other half 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. At the

end of a year, however, the average weight loss for subjects in the two groups was not

significantly different.

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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 average of 5.1 kg in a year. The

subjects in the low-fat diet group lost an average of 3.1 kg in a year. Explain how this

information could be consistent with the fact that weight loss in the two groups was

not significantly different.

Short answer

For eliminating confounding

Step-by-step solution

Given Information

researchers randomly assign the subjects to the diet treatments.

Explanation:

When the effects of two variables on the same response variable cannot be distinguished, they are said to be confused.

Given Information:

“lost significantly more weight”

Explanation:

The low-carbohydrate diet and the low-fat diet were assigned to patients at random.

Given Information:

The subjects in the low-carb diet group lost an average of 5.1 kg in a year. The

subjects in the low-fat diet group lost an average of 3.1 kg in a year.

Explanation:

Patients are randomly assigned to therapies, ensuring that the different treatment groups are as identical as feasible prior to therapy, preventing confounding.

For example, if one of the groups had higher weights and cholesterol levels before the treatment, that group is more likely to have a larger change in weight and cholesterol levels after the treatment (as their weights and cholesterol levels can decrease more).