350 Chapter 8:Hypothesis Testing
smoking and heart attacks. Given that- Older people are at greater risk of heart disease than are younger people; and
- As a group, smokers tend to be somewhat older than nonsmokers;
would the scientist be justified in her conclusion? Explain how the experi-
mental design can be improved so that meaningful conclusions can be drawn.
72.A researcher wants to analyze the average yearly increase in a stock over a 20 year
period. To do so, she plans to randomly choose 100 stocks from the listing of
current stocks, discarding any that were not in existence 20 years ago. She will then
compare the current price of each stock with its price 20 years ago to determine
its percentage increase. Do you think this is a valid method to study the average
increase in the price of a stock?