=+58. Dentists make many people nervous (even more so than statisticians!). To assess any effect of such nervousness on blood pressure, the systolic blood pressure of each of 60 subjects was measured both in a dental setting and in a medical setting (“The Effect of the Dental Setting on Blood Pressure Measurement,” Amer. J. of Public Health, 1983:

1210–1214). For each subject, the difference between dental setting pressure and medical setting pressure was computed; the resulting sample mean difference and sample standard deviation of the differences were 4.47 and 8.77, respectively.

Estimate the true average difference between blood pressures for these two settings using a 99%

confidence interval.