A study was done on 41 first-year medical students to see if their anxiety levels changed during the first semester. One measure used was the level of serum cortisol, which is associated with stress. For each of the 41 students the level was compared during finals at the end of the semester against the level in the first week of classes. The average difference (end of semester minus beginning) was +2.08 with a standard deviation of 7.88. Find a 95% lower confidence bound for the population mean difference μ. Does the bound suggest that the mean population stress change is necessarily positive?