Personnel officer: The exorbitant cost of our health-insurance benefits reflects the high dollar amount of medical expenses incurred by our employees. Employees who are out of shape, as a group, have higher doctor bills and longer hospital stays than do their colleagues who are fit. Therefore, since we must reduce our health-insurance costs, we should offer a rigorous fitness program of jogging and weight lifting to all employees, and require employees who are out of shape to participate.
The conclusion reached by the personnel officer depends on which of the following assumptions?