1. In early 2007 a larger than usual number of cats and dogs developed kidney failures, and many died. Initially, researchers did not know why so they located some of the pets who had gotten sick and ask their owners about diets, exposure to toxins, and other possible causes.

a. Is this an example of an experiment or observational study?

b. What is the explanatory variable(s) and the response variable(s)?

c. Is it a prospective or retrospective?

d. In the process of their investigation, they believe that the cause of the illness is due to an unknown toxin in the food of a popular pet brand. Explain, what steps must the researchers take to show that indeed the pet food brand caused the illnesses and death.

2. A group of disabled women ages 65 and older were followed for several years. It was found that those who had a vitamin B12 deficiency were twice as likely to suffer from severe depressions than those who did not.

a. Describe the type of study being performed.

b. Describe the explanatory variable(s) and response variable(s).

c. Is this a prospective or retrospective study?

d. Can the conclusion be made that a vitamin B12 deficiency leads to depression? Explain.

e. Can you think of any lurking variables that could have led to this conclusion?

3. Researchers investigated over a 4-month period the effects of omega-3 fats from fish oil and whether it helps improve anxiety. Participants were randomly selected and assigned to a group from a list of volunteers with similar characteristics: 30 were given a high dose of 10 g/day while another group of the same size was given 0 g/day. None of the participants were informed on the type of does that they received.

a. Describe the type of study being performed.

b. Identify the factor(s) and the response variable(s).

c. Does this study contain blocking?

d. What is blocking and why do researchers use it?

e. Is this a blind or double-blind study? Explain what the difference is between the two.

f. Is there a control being used in the study? Explain.