Table 3.

Covariance analysis of FVC%, FEV1%, FEV1/FVC% in different PPD-exposure group (mean ± SD).

Variable	Lower exposure (n = 24)	Middle exposure (n = 50)	Higher exposure (n = 50)	F	P value
FVC%	103.044 ± 9.498	89.076 ± 11.806*#	101.399 ± 9.409	7.519	< 0.001
FEV1%	104.665 ± 12.289	91.772 ± 6.261*	92.483 ± 10.300*	8.791	< 0.001
FEV1/FVC%	102.215 ± 14.040	104.700 ± 14.779#	91.889 ± 12.737*	6.855	< 0.001

Measurement indexes of capacity and the volume of lung include forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and ratio of FEV1 to FVC (FEV1/FVC), etc. Abnormal pulmonary function is defined as: FVC% (percentage of forced vital capacity, FVC measured value/FVC predicted value) < 80%; FEV1% (percentage of forced expiratory volume in 1 s, FEV1 measured value/FEV1 predicted value) < 75%; FEV1/FVC%, FEV1 measured value/FVC measured value < 70%. The predictive values of FVC or FEV1 is automatically calculated by the pulmonary function analyzer according to age, gender, height, weight and race.

*P < 0.05, comparison of the higher and middle exposure group with the lower exposure group by Bonferroni method.

^#P < 0.05, comparison between the higher exposure group and middle exposure group by Bonferroni method.

The covariant variables including gender, ethnic group, working age, education condition and recent hair dye history.