The more cigarettes a person has smoked over his or her lifetime, the greater the probability that the person has developed lung cancer.
(a) What is the direction of the correlation between these two variables?
(b) This finding does not, by itself, prove that smoking causes lung cancer. Why not?
(c) If smoking does not cause lung cancer, what might explain the correlation between the two variables?
(d) Medical authorities believe that a causeand-effect relationship between smoking and lung cancer has been proven well beyond reasonable doubt. What kind of evidence do you think has persuaded them?