Emotional stress is a well known cause of certain serious health problems, including high blood pressure and cardiac complications. Now, an additional concern can be added to the list of maladies caused by emotional stress. A recent study surveyed both people who have high levels of emotional stress and people who don’t, and found that people with high emotional stress levels are significantly more obese and nervous than people with lower levels of emotional stress.

Which of the following is an assumption on which the argument rests?