3. “Low-carb” diets have become quite popular recently. In a recent study report

Question

3. “Low-carb” diets have become quite popular recently. In a recent study reported in the New England Journal of Medicine, researchers randomly assigned 63 obese men and women to either a low-carbohydrate diet or a conventional diet. Each subject’s weight loss, as a percentage of body weight, was recorded after 3 months, after 6 months, and after 12 months.

a. Is this an observational study or an experiment? Explain briefly.

b. Identify the explanatory variable and the response variable.

c. Some people exercise more than others, and exercise can affect weight loss. Explain why this exercise level is nevertheless not a confounding variable in this study.

d. The researchers wanted to test the claim that people tend to lose more weight on low-carb diets than on conventional diets. Write the null and alternative hypotheses (in symbols only) for testing this claim.

e. The p-values were .182 for the 3-month weight losses, .106 for the 6-month weight losses, and .070 for the 12-month weight losses. Summarize the conclusions you would draw.

Explanation / Answer

a)it is an experiment. An experiment is a method of applying treatments to a group and recording the effects.

c)a confounding variable (also confounding factor, a confound, orconfounder) is an extraneous variable in a statistical model that correlates (directly or inversely) with both the dependent variable and the independent variable. exercise is dependent on person.

d)For each case, (3-,6-, or 12- months)
H0: no difference in mean weight loss (low-conv)
HA: diff >0
At level 0.01, first 2 cases are significant, the last is not.
e)The claim that people tend to lose more weight on low-carb diets than on conventional diets are supported in 3- and 6- months cases, but not in 12-month case.

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