A medical researcher wants to investigate the relationship between increased dietary intake of fiber and cholesterol level. The four treatments being studied are a control treatment where a subject maintains their current diet and three increased fiber treatments where a subject increases their dietary intake of fiber by either 10%, 20%, or 25%. A simple random sample of size 200 is selected from a list of 500 volunteers to make up the pool of experimental units. Each subject will have their cholesterol level measured prior to the start of the experiment to serve as a baseline comparison and then again after a 3-month treatment period, and the change in cholesterol level after the 3-month treatment period will be studied. The 200 subjects are randomly assigned to the four groups and the subjects are given detailed instructions on how they are to alter their dietary regimen.

(a) Is this study an experiment or an observational study? Why?

(b) What are the treatments in this study?

(c) What are the experimental units in this study?

(d) What is the response variable in this study?