Table 1.

Characteristics of the study population

Variable	Respondents (n = 3,840, 86.8%), n (%)a	Nonrespondents (n = 585, 13.2%), n (%)a	Total (n = 4,425, 100%), n (%)a	p value
Age group				< 0.0001
Missing	8	80	88
18–39 years	136 (82.4)	29 (17.6)	165 (100)
40–49 years	644 (91.3)	61 (8.7)	705 (100)
50–59 years	1,060 (89.8)	120 (10.2)	1,180 (100)
60–69 years	1,147 (90.1)	126 (9.9)	1,273 (100)
70–79 years	676 (86.4)	106 (13.6)	782 (100)
80 years and older	169 (72.8)	63 (27.2)	232 (100)
Affected breast				0.124
Missing	162	22	184
Right	1,764 (86.6)	273 (13.4)	2,037 (100)
Left	1,823 (87.2)	268 (12.8)	2,091 (100)
Both	91 (80.5)	22 (19.5)	113 (100)
UICC staging				< 0.0001
Missing	686	119	805
Stage 0	157 (92.9)	12 (7.1)	169 (100)
Stage I	1,403 (89.8)	159 (10.2)	1,562 (100)
Stage II	1,110 (85.2)	193 (14.8)	1,303 (100)
Stage III	351 (82.4)	75 (17.6)	426 (100)
Stage IV	133 (83.1)	27 (16.9)	160 (100)
Grading				0.562
Missing	418	52	470
G1	572 (87.3)	83 (12.7)	655 (100)
G2	1,994 (86.7)	306 (13.3)	2,300 (100)
G3	856 (85.6)	144 (14.4)	1,000 (100)
ASA classification				< 0.0001
Missing	311	37	348
1 (normal health)	1,734 (89.1)	212 (10.9)	1,946 (100)
2 (mild systemic disease)	1,484 (86.3)	235 (13.7)	1,719 (100)
3–5 (severe systemic disease to moribund)	311 (75.5)	101 (24.5)	412 (100)
Neoadjuvant chemotherapy				0.858
Missing	257	26	283
Received	264 (86.8)	40 (13.2)	304 (100)
Not received	3,319 (86.5)	519 (13.5)	3,838 (100)
Type of surgery				< 0.0001
Missing	270	37	307
Mastectomy	929 (81.6)	210 (18.4)	1,139 (100)
Breast conserving	2,641 (88.7)	338 (11.3)	2,979 (100)

^aAbsolute frequency (% of total in each category).