Table 2. Confidence intervals for the calculated non-linear distortions index T in the measured groups.

Std denotes standard deviation.

Group	Min	Max	Mean	Std
COPD-GOLD II	0.7579	0.9840	0.8228	0.0488
COPD-GOLD III	0.8893	0.9568	0.9205	0.0229
COPD-GOLD IV	0.9836	1.0459	1.0019	0.0214