Scottish researchers compared rates of depression between 94 undergraduates who regularly kept diaries and 41 students who did not. They found that people who kept diaries were more likely to have depression than those who did not. The researchers said, "We expecte diary-keepers to have some benefit, or be he same, but they were the worst off. You are probably much better if you don't write anything at all." Why is this an incorrect interpretation of these results?