Table 1 Prematching and postmatching baseline characteristics

Male

44 (57.9%)

97 (61.8%)

37 (58.7%)

79 (62.7%)

Age, year, mean ± SD

63.95 ± 13.13

63.82 ± 12.19

63.75 ± 12.92

63.28 ± 12.73

BMI

  > 25 kg/m²

28 (36.8%)

62 (39.5%)

21 (33.3%)

48 (38.1%)

  ≤ 25 kg/m²

48 (63.2%)

95 (60.5%)

42 (66.7%)

78 (61.9%)

Alb, g/L, mean ± SD

36.53 ± 5.17

35.95 ± 5.24

36.65 ± 5.14

36.18 ± 4.89

Hb, g/L, mean ± SD

121.27 ± 12.98

119.52 ± 13.26

119.53 ± 12.75

118.95 ± 13.13

Tumor size, cm, mean ± SD

3.48 ± 1.73

3.64 ± 1.57

3.65 ± 1.64

3.47 ± 1.68

Height of distal edge of the tumor, cm, mean ± SD

0.034

0.615

4.21 ± 2.16

4.85 ± 2.14

4.26 ± 2.26

4.44 ± 2.20

Tumor location

 Low rectum (< 5 cm)

53 (69.7%)

87 (55.4%)

43 (68.3%)

82 (65.1%)

 Middle rectum (5.1–10 cm)

23 (30.3%)

70 (44.6%)

20 (31.7%)

44 (34.9%)

ASA score

 I

15 (19.7%)

34 (21.7%)

11 (17.5%)

28 (22.2%)

 II

48 (63.2%)

94 (59.9%)

42 (66.7%)

80 (63.5%)

 III

13 (17.1%)

29 (18.4%)

10 (15.8%)

18 (14.3%)

Preoperative serum CEA, ng/ml, mean ± SD

0.734

0.792

6.60 ± 3.17

6.44 ± 3.27

6.64 ± 3.28

6.77 ± 3.16

Clinical stage

 I

17 (22.4%)

32 (20.4%)

14 (22.2%)

21 (16.7%)

 II

23 (30.3%)

51 (32.5%)

22 (34.9%)

46 (36.5%)

 III

36 (47.3%)

74 (47.1%)

27 (42.9%)

59 (46.8%)

Degree of histological differentiation

0.715

0.847

 Well

11 (14.5%)

17 (10.8%)

7 (11.1%)

12 (9.5%)

 Moderate

49 (64.5%)

107 (68.2%)

44 (69.8%)

93 (73.8%)

 Poor + undifferentiated

16 (21.0%)

33 (21.0%)

12 (19.1%)

21 (16.7%)

Neoadjuvant chemoradiation

54 (71.1%)

85 (54.1%)

39 (61.9%)

71 (56.3%)

Assistant's experience

  > 5 years after resident training

21 (27.6%)

46 (29.3%)

16 (25.4%)

36 (28.6%)

  ≤ 5 years after resident training

55 (72.4%)

111 (70.7%)

47 (74.6%)

90 (71.4%)