Is FEV1determined in a plethysmograph a better indication of obstructive lung disease than FEV1determined by a spirometer?

in a current paper in the Journal of Applied Physiology ([3][1]) the authors have tried to find out whether the compression of the gas in the lungs during a forced expiration influences the grading of decreased lung function in patients with sick lungs either due to emphysema or chronic bronchitis.