Do Diets Work? CW

The Atkins Diet is one of many popular weight loss diets. It is based on reducing the consumption of carbohydrates. For years, such "low-carb" diets have been touted as being effective for weight loss and other health benefits. But before 2001, no one had attempted to demonstrate the effectiveness of a low-carb diet in a well-designed comparative experiment. Then, two separate groups of researchers attempted to do just that.

At Duke University Medical Center, Dr. William Yancy and his colleagues recruited 120 people between the ages of 18 and 65. All of the participants were obese and had high cholesterol, but were otherwise in generally good health. Researchers randomly assigned half of the participants to a low-carbohydrate, high-protein diet (similar to an Atkins Diet) and the other half to a low-fat, low-cholesterol diet. At the end of six months, researchers measured the change in each participant's weight and cholesterol levels.

In the second study, Dr. Linda Stern and her colleagues recruited 132 obese adults at the Philadelphia Veterans Affairs Medical Center in Pennsylvania. Half of he participants were randomly assigned to a low-carbohydrate diet and the other half were assigned to a low-fat diet. Researchers measured each participants change in weight and cholesterol level after six months and again after one year.

1). Complete the following table using the details provided above about the two studies.

	Duke University Study	Philadelphia Study
Subjects
Explanatory Variable(s) (x causes y, explanatory is x)
Treatments
Response Variable(s) (x causes y, response is y)

2). Draw the experimental design in the Duke University study.

3). Draw the experimental design in the Philadelphia study.

4). Explain why both of these studies are experiments and not observational studies.

5). Give an example of a variable in one of the two experiments that could cause confounding. How could the variable you chose affect the results?