. 2004 Jun;39(3):693–694. doi: 10.1111/j.1475-6773.2004.00251.x

Table 3.

Instrumental Variable and OLS Estimates of the Effectiveness of Breast Conserving Surgery plus Irradiation on Survival Relative to Mastectomy

					After diagnosis, effect of BCSI on patient survival

Row	Analysis Method	Instruments Specified	Number of groups per instrument	Instrument F-statistic	1 year	2 years	3 years	4 years
1	Unadjusted OLS	none	na	na	0.01	0.02	0.04^**	0.06^**
2	Adjusted OLS^#	none	na	na	−0001	−0003	−00001	0.007
3	Instrumental Variable Estimates^#	BCSI Rate	2	8.57^***	−0.32	−0.68	−0.57	−0.51
4			4	5.19^***	−0.37^**	−0.54^**	−0.45	−0.65^*
5			8	3.43^***	−0.33^**	−0.50^**	−0.46^*	−0.52^*
6			12	3.00^***	−0.23^**	−0.41^**	−0.33	−0.11
7		Radiation Distance	2	21.79^***	−0.21^*	−0.12	−0.33	−0.23
8			4	7.52^***	−0.14	−0.22	−0.39	−0.38
9			8	3.30^***	−0.14	−0.19	−0.35	−0.28
10			12	2.94^***	−0.05	−0.14	−0.33	−0.40^*
11		BCSI Rate & Radiation Distance	2	13.08^***	−0.24^**	−0.25	−0.38^*	−0.30
12			4	4.99^***	−0.24^**	−0.32^*	−0.39^*	−0.45^*
13			8	2.76^***	−0.24^**	−0.31^**	−0.34^*	−0.27
14			12	2.74^***	−0.12^*	−0.23^**	−0.30^**	−0.15

^***,**,*

statistically significant at .99, .95, and .90 confidence, respectively.

Models also specified binary variables for age groups (<50, 50–64, 65–69, 70–74, 75–79, 80–84, 85+), tumor sizes (<2 cm, 2–5 cm, 5+cm), positive lymph node involvement, tumor grade groups (1, 2, 3, 4, 9–unknown), tumor location groups (nipple, central portion, upper-inner quad, lower-inner quad, upper-outer quad, lower-outer quad, axillary tail, overlapping lesion, not-stated), Charlson commorbidity index (0, 1, 2, 3+), residence zip code poverty percentage (#7, 7–10, 10–13, 13–20, >20), distance from residence to nearest hospital (#2.83, 2.83–9, 9–15, >15), payer (Medicaid, Medicare, Blue Cross/Blue Shield, other private, other government, self pay), and year of diagnosis (1989, 1990, 1991, 1992, 1993, 1994).