Hoaglin, Mosteller, and Tukey (1983) present data on blood levels of beta-endorphin as a function of stress. They took beta-endorphin levels for 19 patients 12 hours before surgery and again 10 minutes before surgery. The data are presented below, in fmol/ml:

12 Hours 10 Minutes Subject Before Before 1 10.0 6.5 2 6.5 14.0 3 8.0 13.5 4 12.0 18.0 5 5.0 14.5 6 11.5 9.0 7 5.0 18.0 8 3.5 42.0 9 7.5 7.5 10 5.8 6.0 11 4.7 25.0 12 8.0 12.0 13 7.0 52.0 14 17.0 20.0 15 8.8 16.0 16 17.0 15.0 17 15.0 11.5 18 4.4 2.5 19 2.0 2.0 Based on these data, what effect does increased stress have on beta-endorphin levels?