A health spa claims that a new exercise program will reduce a person's waist size by 2 centimeters on the average over a 5-day period. The waist sizes of 6 men who participated in this exercise program are recorded before and after the 5-day period in the following table:
Man
1 2 3 4 5 6
Waist Size 90.4 95.5 98.7 115.9 104 85.6
Before
Waist Size 91.7 93.9 97.4 112.8 101.3 84
After
Assuming that the distribution of differences of waist sizes before and after the program to be approximately normal, determine whether the health spa's claim is valid.