—Dr Auchincloss and I appreciate the letter of Dr Baylor and colleagues, since we believe it is essentially a confirmation of our work. The difference in percentage of patients in their series and ours having a spirometrically identified restrictive defect confirmed by older criteria can probably be explained by their use of 75% as the lower limit of normal for the ratio of 1-s forced expiratory volume to forced vital capacity, rather than 70% as we did. This would result in more rigid spirometric criteria for a restrictive defect and, therefore, they should have a somewhat closer matching than we did.
As I stated in the article, there is nothing basically wrong with using spirometric criteria. The important thing is that we recognize the current imprecise nature and nonuniformity of the criteria for a restrictive defect, and perhaps work toward more uniform definitions.