Table 1.

Selected patient characteristics before and after Mahalanobis matching

	Before match					After match
	No SLNB		SLNB		SDa	No SLNB		SLNB		SD
	N	%	N	%	%	N	%	N	%	%
Total sample	13,106	84	2409	16	N/A	4718	66	2409	34	N/A
Age (years)
67–69	2571	20	573	24	− 10.1	981	21	573	24	− 7.2
70–74	4104	31	783	33	− 2.6	1592	34	783	33	2.6
75–79	3367	26	614	25	0.5	1263	27	614	25	2.9
80–84	2110	16	333	14	6.4	670	14	333	14	1.1
85+	954	7	106	4	12.3	212	4	106	4	0.5
Race
White	11,369	87	2148	89	− 7.4	4099	87	2148	89	− 7.0
Black	1032	8	170	7	3.1	386	8	170	7	4.2
Other	705	5	91	4	7.7	233	5	91	4	5.7
Hispanic ethnicity
Yes	545	4	135	6	− 6.7	221	5	135	6	− 4.2
No	12,561	96	2274	94	6.7	4497	95	2274	94	4.2
Marital status
Married	6211	47	1227	51	− 7.1	2286	48	1227	51	− 5.0
Unmarried	6204	47	1085	45	4.6	2196	47	1085	45	3.0
Other	691	5	97	4	5.9	236	5	97	4	4.7
Grade
Well differentiated	2048	16	254	11	15.1	498	11	254	11	0.0
Moderately differentiated	4456	34	629	26	17.3	1371	29	629	26	6.6
Poorly differentiated	2925	22	802	33	− 24.7	1449	31	802	33	− 5.5
Undifferentiated	1070	8	321	13	− 16.7	601	13	321	13	− 1.7
Unknown	2607	20	403	17	8.2	799	17	403	17	0.6
Tumor size
< 2.0 cm	7402	56	1264	52	8.1	2552	54	1264	52	3.2
2.0 to ≤ 5.0 cm	1512	12	434	18	− 18.3	749	16	434	18	− 5.7
> 5.0 cm	179	1	89	4	− 14.9	149	3	89	4	− 2.9
Missing	4013	31	622	26	10.7	1268	27	622	26	2.4
Hormone receptors
ER– and PR–	923	7	341	14	− 23.3	631	13	341	14	− 2.3
ER+ or PR+	5839	45	1329	55	− 21.4	2608	55	1329	55	0.2
Missing	6344	48	739	31	36.9	1479	31	739	31	1.5
Comedonecrosis
Yes	1246	10	297	12	− 9.1	524	11	297	12	− 3.8
No	11,860	90	2112	88	9.1	4194	89	2112	88	3.8
Disability
Yes	410	3	67	3	2.0	129	3	67	3	− 0.3
No	12,696	97	2342	97	− 2.0	4589	97	2342	97	0.3
Elixhauser comorbidity
None	6321	48	1219	51	− 4.7	2229	47	1219	51	− 6.7
1 to 2	5177	40	935	39	1.4	1914	41	935	39	3.6
3 or more	1608	12	255	11	5.3	575	12	255	11	5.0
Surgeon volumeb
1	6243	48	1140	47	0.6	2182	46	1140	47	− 2.2
2	3114	24	578	24	− 0.5	1099	23	578	24	− 1.6
3	1645	13	329	14	− 3.3	596	13	329	14	− 3.0
4+	1865	14	300	12	5.2	727	15	300	12	8.5
Not assigned	239	2	62	3	− 5.1	114	2	62	3	− 1.0
Year of diagnosis
1998–1999	1039	8	30	1	32.4	63	1	30	1	0.8
2000–2001	1959	15	140	6	30.3	286	6	140	6	1.1
2002–2003	2011	15	255	11	14.2	520	11	255	11	1.4
2004–2005	2163	17	431	18	− 3.7	863	18	431	18	1.0
2006–2007	2021	15	508	21	− 14.7	986	21	508	21	− 0.5
2008–2009	2007	15	539	22	− 18.1	1048	22	539	22	− 0.4
2010–2011	1906	15	506	21	− 17.0	952	20	506	21	− 2.0
Geographic region
Midwest	1980	15	296	12	8.2	583	12	296	12	0.2
Northeast	3217	25	488	20	10.3	979	21	488	20	1.2
South	2408	18	588	24	− 14.8	1141	24	588	24	− 0.5
West	5501	42	1037	43	− 2.2	2015	43	1037	43	− 0.7

SLNB sentinel lymph node biopsy

^aSD refers to standardized difference, which is a statistic that evaluates the balance of matched cohorts. Standardized difference below 10% indicates balance on the variable

^bSurgeon volume reflects women who saw a provider who performed BCS on X number of women in our sample for the year of this woman’s surgery