Appraisal of a new test: Between-technician variation in the measurement of closing volume

To determine the between-technician variation in the measurement of closing volume, 24 subjects were divided into 3 blocks of 8 subjects each. Each block was then tested by a pair of technicians. Each of the 3 technicians involved in the study tested 16 subjects. It was later necessary to reject the tracings of 2 subjects in one of the 3 blocks, leaving 22 for analysis. The N2 method of determining closing volume was used. The statistical analysis was performed separately on the following measures derived from the tracings: expired vital capacity, planimetry of the area under the curve, total lung capacity, closing volume as a per cent of expired vital capacity, and closing capacity as a per cent of total lung capacity. All tracings were assessed by each technician. Two separate analyses of variance were then carried out to determine, respectively, the components of variance in the administration of the test and in the interpretation of the tracings. Because different persons were able to administer the test the same way, it seems that closing volume poses no problem in administration, provided that instructions as to how to perform the test are closely followed. In the interpretation of the tracings, significant differences were found for all measures, except planimetry; however, not all of these have the same practical implications. Some tracings were found "difficult" to interpret and contributed more to the over-all variation than did others. When making use of a new test in a population study, the between-technician variation should be determined before the study is begun.