Table 3 in the article (Brooks, Chrischilles, Scott, Chen-Hardee, “Was Lumpectomy Underutilized for Early Stage Breast Cancer?—Instrumental Variables Evidence for Stage II Patients from Iowa,” 2003, Health Services Research 38 (6):1385–1402) contained two typographical mistakes that could lead to a misinterpretation of the results. The sign of all instrumental variable (IV) estimates should be negative as in the updated table below. Note that two parameter estimates reported as positive and significantly different from zero statistically are actually negative and significantly different from zero statistically.
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).