A study looked at the annual number of days of restricted activity (for example, missing work or staying in bed for more than half a day because of injury or illness)

for men with different cigarette-smoking histories [27]:

These data suggest that it is best never to smoke, but once you start smoking, it’s better not to stop.

a. Explain why there might be sampling bias in this study.

b. Suppose that smoking is bad for your health. Explain how it could still be the case that people who quit smoking are in worst health than people who keep smoking.

c. What would have to be done to have a controlled experiment?

Transcribed Image Text:

Never smoked 14.8 days Currently smoking 22.5 days Quit smoking 23.5 days