Clinical depression is linked to several other diseases. Scientists at Johns Hopkins University undertook a study to determine whether heart disease is one of these. A group of 1190 male medical students was tracked over a 40-year period. Of these, 132 had suffered clinically diagnosed depression. For each student, the scientists recorded whether the student died of a heart attack (code = 2) or did not (code = 1).
a. Can we infer at the 1% significance level that men who are clinically depressed are more likely to die from heart diseases?
b. If the answer to part (a) is “yes” can you interpret this to mean that depression causes heart disease? Explain.