Question

3. There are studies that show an association between liver cancer and smok-

ing. However, alcohol consumption is a confounding variable. This means

(choose one option, and explain):

(a) Alcohol causes liver cancer

(b) Drinking is associated with smoking, and alcohol causes liver cancer.

4. The National Highway and Trac Safety Administration analyzed thefts

of new cars in 2002, as well as sales gures for that year. It found that

99 Corvettes and 26 Inniti Q45 sedans were stolen in 2002. Should we

conclude that thieves like American cars better, or do we need some more

information?

5. A new program to rehabilitate prisoners before their release: the object is

to reduce the recidivism rate - the percentage who will be back in prison

within two years of release. The program involves several months of \boot

camp" - military style basic training with very strict discipline. Admission

to the program is voluntary, and a prison spokesperson said that \Those

who complete boot camp are less likely to return to prison than other

inmates."

(a) What are the treatment and control groups in the spokesperson's

comparison?

(b) Is the spokesperson's statement based on a randomized controlled

experiment or an observational study?

(c) Can we use the spokesperson's statement to conclude that the pro-

gram worked? Explain your answer.

Answer 1

(3) (b) Drinking is associated with smoking, and alcohol causes liver cancer.

confounding variable influences both the dependent variable and independent variable causing a spurious association. Confounding difficult to be described in terms of correlations or associations.

(4) yes, we need some more information.

(5a) treatments is :several months of \boot camp" - military style basic training with very strict discipline.

control group: other inmates who donot participate in camp

(5b)an observational study

(5c)yes, program worked as the

Those who complete boot camp are less likely to return to prison than other inmates."