The use of vital capacity measurements of the lungs in a comparative way implies a certain standard of reliability of the measurements on the normal subject. If the observations made on the normals cover a wide range of variability, then small differences, such as may well arise from moderate disturbances in function, will be obscured, and the practical value of the test greatly diminished.
In adults the limitations and practical usefulness of vital capacity measurements have been clearly shown in the work of Peabody,1 West2 and others. More recently, we have applied the test to children and have indicated a line of usefulness in this field.3 A question concerning the reliability of the results naturally arises, however, when vital capacity measurements are made on young subjects, since there are two outstanding ways in which the test, as applied to children, may be expected to yield more variable results than when
EDWARDS DJ, WILSON MG. AN ANALYSIS OF SOME OF THE FACTORS OF VARIABILITY IN THE VITAL CAPACITY MEASUREMENTS OF CHILDREN. Arch Intern Med (Chic). 1922;30(5):638-647. doi:10.1001/archinte.1922.00110110109011