1. Why can't you design a controlled experiment to determine whether smoking causes lung cancer?
2. An economist wishes to determine if a particular advertising campaign
for cigarrettes affected children's decisions to smoke. To do this,
he looks
through a national database that counted the number of children who
said they smoked each year from 1980 through 1995. He then compared
these smoking rates before and after the advertising campaign. Is
this an observational or controlled study? Why?
3. A report of a study in the LA Times said that neighborhoods with a high number of liquor stores per capita also have a high crime rate when compared to neighborhoods with a relatively low number of liquor stores per capita. Is this an observational or controlled study? Why? Can we conclude that removing the liquor stores from the high-crime neighborhoods would lower the crime rate?
4. The LA Times (November 1997) reports that "A new study in the May
1 New England Journal of Medicine provides some of the strongest evidence
yet that regular exercise helps protect women from breast cancer.
The research, conducted in Norway, found that women who exercise at least
four hours a week have a breast cancer risk about one-third lower than
usual." Can we conclude that exercise prevents breast cancer?
Why or why not?