A certain oat cereal manufacturer boasts that adults who eat its cereal every day have lower cholesterol levels. To test this claim, a nurse measures the cholesterol levels of 18 patients. These patients are instructed to eat the oat cereal every day for four weeks. At the end of this four-week period, the nurse measures the cholesterol levels again. The differences in cholesterol levels (before – after) are listed. A negative difference means that a patient’s cholesterol level increased over the four weeks.–18, 5, 9, –1, 0, 4, 3, –2, 0, 11, 5, 12, –5, 1, –3, 4, 8, 9