5) A doctor has begun to recommend a new over-the-counter herbal/vitamin/fiber dietary supplement to his weight-loss patients. Over the course of the year, 14% of his patients report that they are using it consistently, another 42% say they tried it but found it too expensive, and the rest say they never tried it at all. At the end of the year, the doctor notes that those who kept using the supplement had a greater average weight loss than those who did not. He concludes that the supplement is effective in achieving weight loss. Referring to principles of experimental design, identify at least one flaw in the doctor's research methodology which may invalidate his conclusions, and explain how to conduct an experiment that avoids this flaw.

6) A market researcher wants to do a survey on consumer preferences in Oneida County. He obtains the Utica and Rome telephone directories and calls every tenth number listed in the white pages. 18% of the calls result in someone willing to give information.

a) Identify the population and the sample in this study.

b) Identify any possible sources of bias in this sampling procedure. If there are none, say so.