Table 3. Factors associated with prolonged operation time.

	Prolonged operation time
	Univariate, Coefficient (95 %CI)	P value	Multivariate, Coefficient (95 %CI)	P value
First period
Age, years	– 0.08 ( – 0.19 to 0.03)	0.15
Male sex	0.04 ( – 3.34 to 3.43)	0.98
Rectal lesion	– 0.41 ( – 4.27 to 3.46)	0.83
Fibrosis	5.90 (2.36 to 9.44)	0.002	5.90 (2.36 to 9.44)	0.002
Large nodule	0.48 ( – 3.25 to 4.20)	0.80
Central depression	– 0.53 ( – 7.94 to 6.88)	0.89
Presence of adenocarcinoma	– 1.96 ( – 5.23 to 1.32)	0.23
Submucosal invasion	1.38 ( – 2.33 to 5.08)	0.46
Latter period
Age, years	– 0.05 ( – 1.23 to 0.03)	0.20
Male sex	1.56 ( – 0.27 to 3.39)	0.09
Rectal lesion	– 0.91 ( – 4.33 to 2.52)	0.60
Fibrosis	0.68 ( – 1.34 to 2.70)	0.50
Large nodule	– 0.79 ( – 3.31 to 1.74)	0.53
Central depression	1.48 ( – 0.85 to 3.82)	0.21
Presence of adenocarcinoma	0.75 ( – 1.33 to 2.83)	0.47
Submucosal invasion	1.76 ( – 0.92 to 4.43)	0.19

CI, confidence interval; P values were analyzed using univariate and multivariate linear regression analyses.