To reduce productivity losses from employees calling in sick, Corporation X implemented a new policy requiring employees to come into work unless they were so sick that they had to go to a doctor. But a year after the policy was implemented, a study found that Corporation X's overall productivity losses due to reported employee illnesses had increased. Which of the following, if true, would best explain why the policy produced the reverse of its intended effect? ['Employees coming into work when sick often infect many of their coworkers.', 'After the policy was implemented, employees more frequently went to the doctor when they felt sick.', 'Before the policy was implemented, employees who were not sick at all often called in sick.', 'There are many other factors besides employee illness that can adversely affect productivity.']