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Chapter 4: Q 74. (page 257)

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.

Short Answer

Expert verified

(a) This is because randomization is one of the three principles of experimental design.

(b) It means that the difference in weights is large and it cannot be just by chance.

(c) The total weight difference is 2kg over a period of year which can be by chance.

Step by step solution

01

Given Information

132participants were assigned diets randomly to obtain results for weight loss.

An experiment was conducted in which half participant was given low carbohydrate diet and half were given low fat diet. to examine change in weight and cholesterol. The participant in low carb diet lost an average of5.1 kg and subjects in low fat diet lost an average of3.1kg.

02

To explain why did researchers randomly assign the subjectsto the diet treatments

An experiment was conducted in which half participant was given low carbohydrate diet and half were given low fat diet. to examine change in weight and cholesterol. The researchers randomly assign the subjects as randomization is one of the three principles of experimental design. It is also done to make sure that different groups are as similar as possible.

03

To explain “lost significantly more weight” to one who don't understand statistics.

As the context of above experiment, 鈥渓ost significantly more weight鈥� means the difference in weight loss is large that cannot be due to chance and cannot be ignored.

04

To explain how this information could be consistent with the fact that weight loss in the two groups was not significantly different.

As per the results, the participant in low carb diet lost an average of 5.1kg and subjects in low fat diet lost an average of 3.1kg.

The total difference in weight loss was 2kg that appeared over a period of an year. This could be due to chance. Hence weight loss is not statistically significant.

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