For the test, patients were treated on one day with the mechanical device and on the following day with manual chest percussion. All patients received identical treatments on any given day during the test. The test results found that the youngest of the subjects who could use the mechanical device effectively without assistance was 13 years old. Among all of those patients who could use the mechanical device effectively, all but one preferred the mechanical device to the manual method of chest percussion. With one exception also, the parents of the subjects preferred the use of the mechanical device to the manual method. Based on sputum measurements, the researchers concluded that the mechanical device was as effective as the manual methods of chest percussion (Maxwell & Redmond, 1979).

The researchers exercised sufficient care in the design and implementation of the test to minimize the potential for test bias. The research sample, however, was of some concern. First, the sample was quite small. Second, and of greater importance, the research sample was not selected through the application of random procedures. This absence of randomness in the selection of the sample precluded any generalization of the test findings to a population of subjects wider than the test sample subjects.

Where all of the patients included in the Maxwell and Redomond (1979) test sample were in remission from their cystic fibrosis, however, the subjects included in the 1981 test sample were not in remission. In the Pryor, Parker, and Webber (1981) study, 13 of the 14 subjects had been admitted to hospital for acute exacerbation of their bronchopulmonary infection, while the fourteenth subject had been admitted to hospital for an initial assessment. Of the 14 subjects, two refused to participate in the test and were withdrawn from the research sample. Of the 12 subjects remaining in the test sample, nine subjects "required intravenous antibiotics and three required only oral antibiotics" (Pryor, Parker, & Webber, 1981, p. 123).

(1981) reported on a test of the Salford percussor two years subsequent to the Maxwell and Redmond (1979) study. As was true of the Equi-Med percussor tested by Maxwell and Redmond (1979), the purpose of the Salford percussor was to permit cystic fibrosis patients to perform their own chest therapies, as opposed to depending upon the manual performance of chest percussion by health care professionals. In this test of a mechanical device also, 14 subjects were included in the research sample. The 14 subjects in this test sample, however, were somewhat older than were the subjects in the earlier test sample. The subjects in the 1981 test sample ranged in age from 15 years old to 24 years old, with a mean subject age of 19 years old.