This student project on osteoporosis shows the use of regression analysis and some of its limitations.

1) Women have higher rates of osteoporosis than men, as the regression analysis shows.

2) Physical activity reduces bone decalcification, but people with decalcified bones tend to exercise less. The regression analysis doesn’t show a significant relation.

Health insurance actuaries have a similar question: Does better health (such as by not smoking) raise or lower long-term health insurance costs? People who smoke have more lung cancer, which raises costs. But these people also die earlier, reducing costs of old age chronic diseases. Some actuaries conclude that smoking raises mortality rates and reduces long-term health insurance costs.