### Exercise 1: Vitamin supplements

Exercise 1.30 on page 35.

**Write your answer here**
A) this is an experimental study.  While each patient in the study was observed for their symptoms, each subject was assigned to one of the three treatment groups or to the placebo group.
B) The explanatory variables are 1g vitamin C, 3g vitamin C, and 3g vitamin C plus additives, as well as the placebo group.  The response variables are cold duration and severity of the cold.
C) Yes the patients were blinded for the treatment, they didn't know which group they were assigned to.
D) Yes this was a double blind study, the researches assessing the patients didn't know which group the patients were in.
E) No this doesn't introduce a confounding variable since these people can ultimately be ruled out of the study since they don't contribute to the overall dataset.

### Exercise 2: Income and Education in U.S. countries

Exercise 1.40 on page 37. For part (c), be sure to clearly make a confounding variable argument.

**Write your answer here**
A) The explanatory variable is the percent of the population with a bachelors degree and the response variable is the per capita income.
B) There is a fairly strong, positive relationship between the two variables.  ???
C) No we cannot conclude that having a bachelors degree increases income.  A confounding variable in this argument is also the duration people have been at the job.  People with bachelors degrees tend to stay with the same job for longer periods of time, which also increases the amount one makes at a job.