Chapter 9, Problem 23P

An instrument that is used in some blood-pressure studies is the random-zero device, in which the zero point of the machine is randomly set with each use and the observer is not aware of the actual level of blood pressure at the time of measurement. This instrument is intended to reduce observer bias. Before using such a machine, it is important to check that readings are, on average, comparable to those of a standard cuff. For this purpose, two measurements were made on 20 children with both the standard cuff and the random-zero machine. The mean systolic blood pressure (SBP) for the two readings for each machine are given in Table 9.13. Suppose observers are reluctant to assume that the distribution of blood pressure is normal.

Table 9.13 Comparison of mean SBP with the standard cuff vs. the random-zero machine (mm Hg)

Conduct the test recommended in Problem 9.22

9.22 Which nonparametric test should be used to test the hypothesis that the mean SBPs for the two machines are comparable?