Variation between observers in the estimation of airway resistance and thoracic gas volume.

Variations in the estimation of airway resistance (Raw) and thoracic gas volume (Vtg) made by different observers using body plethysmography have been investigated. Five observers determined Raw and Vtg in normal subjects using prerecorded signals so that intrasubject variations were eliminated. The slopes of the oscillography tracings required to make the determinations were assessed using a cursor and a scale fitted to the oscilloscope. Significant and consistent differences in Raw determined by different observers were found,with a mean range of 37%. Great care should therefore be taken when comparing results obtained by different observers. The variation between observers measuring Vtg was significant and consistent but of much smaller magnitude than was the case for Raw, having a mean range of 12%.