Table S1: List of Excluded Physician Specialties

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Online Supplementary Appendix

TABLE S1: LIST OF EXCLUDED PHYSICIAN SPECIALTIES... 2

TABLE S2: PHYSICIAN AND PATIENT LOCATION INFORMATION FOR SURGICAL SPECIALISTS...3

TABLE S3: PHYSICIAN AND PHYSICIAN PRACTICE CHARACTERISTICS FOR SURGICAL SPECIALISTS...4

FIGURE S1: DISTRIBUTION OF PERCENTAGE OF MEDICAID PATIENTS FOR SURGICAL SPECIALISTS...6

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Table S1: List of Excluded Physician Specialties

Anesthesiology Pathology-Hematology

Anesthesiology-Addiction Medicine Pathology-Immunopathology Anesthesiology-Critical Care Medicine Pathology-Medical Microbiology

Anesthesiology-Hospice and Palliative Medicine Pathology-Molecular Genetic Pathology Anesthesiology-Pain Medicine Pathology-Neuropathology

Anesthesiology-Pediatric Anesthesiology Pathology-Pediatric Pathology Independent Medical Examiner Radiology-Body Imaging

Pathology-Anatomic Pathology Radiology-Diagnostic Neuroimaging Pathology-Anatomic Pathology & Clinical Pathology Radiology-Diagnostic Radiology Pathology-Blood Banking & Transfusion Medicine Radiology-Diagnostic Ultrasound

Pathology-Chemical Pathology Radiology-Hospice and Palliative Medicine Pathology-Clinical Informatics Radiology-Neuroradiology

Pathology-Clinical Pathology Radiology-Nuclear Radiology Pathology-Clinical Pathology/Laboratory Medicine Radiology-Pediatric Radiology Pathology-Cytopathology Radiology-Radiation Oncology Pathology-Dermatopathology Radiology-Radiological Physics Pathology-Forensic Pathology Radiology-Therapeutic Radiology

Radiology-Vascular & Interventional Radiology

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Table S2: Physician and Patient Location Information for Surgical Specialists

Statewide Surgical Specialists (N=1,562)*

Mean (Standard Deviation)

Coefficient on Medicaid Intensity

95%

Confidence Interval

Coefficient on Medicaid Intensity with

Controls**

95%

Coefficient on Medicaid Intensity

with Controls including Academic Medical

Center***

95%

Confidence Interval Physician ZIP Characteristics

Percent of Insured Population with Medicaid in Hospital Service

Area 20.74 (8.0855) 0.373 [.328,.419] 0.132 [.0927,.171] 0.127 [.0874,.167]

Median Household Income in ZIP 60088 (27946) -1018 [-1213,-823] -257 [-415,-98.5] -229 [-391,-66.2]

Percent of Households Below Poverty Level in ZIP

18.552

(13.766) 0.34 [.258,.422] 0.0551

[-.0143,.125

] 0.0525

[-.0189,.124 ]

Patient ZIP Characteristics

Average Patient ZIP Median Household Income 72284 (12815) -949 [-1018,-880] -565 [-612,-517] -572 [-622,-522]

Average Patient ZIP Percent Below Poverty Line 10.163 (3.465) 0.282 [.262,.302] 0.21 [.191,.229] 0.214 [.195,.233]

Note: *Missing values - Percent of insured population with Medicaid in Hospital Service Area (1); physician ZIP characteristics (42 for income and poverty level) **Controls for average commercial patient HCC score and physician 3-digit ZIP Code are included. ***Controls for practicing in an academic medical center, average commercial patient HCC score, and physician 3- digit ZIP Code are included. 43 observations are missing for practice location in an academic medical center, reducing the number of observations for some variables.

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Table S3: Physician and Physician Practice Characteristics for Surgical Specialists

Statewide Surgical Specialists

Number of Observatio

ns Mean (Standard

Deviation)

Coefficie nt on Medicaid Intensity

95%

with Controls

*

95%

with Controls including Academi

c Medical Center**

95%

Confidence Interval Physician Characteristics

Physician is Sole Proprietor 1,433 13.19 -0.0946 [-.301,.111] 0.00387 [-.226,.234] 0.0383 [-.202,.278]

Years Practicing 1,518 23.777 (11.899) -0.0886 [-.163,-.0145] -0.102 [-.184,-.0205] -0.102 [-.184,-.0205]

Board Certified 1,519 84.86 -0.172 [-.416,.0726] -0.217 [-.5,.0646] -0.227 [-.506,.0527]

Practice Location is in Academic Medical Center 1,519 21.92 0.235 [-.011,.482] 0.119 [-.146,.384] - -

Graduated from International Medical School 1,519 12.38 0.255 [.0502,.46] 0.188 [-.0542,.431] 0.193 [-.0507,.437]

Ranking of Medical School (US News and World Report)

for US Medical Graduates 1,205 37.919 (27.858) 0.19 [.0052,.374] 0.0745 [-.146,.295] 0.0699 [-.146,.286]

Practice Style Characteristics

Average Patient Age 1,562 47.338 (3.7092) -0.166 [-.185,-.146] -0.215 [-.239,-.191] -0.226 [-.251,-.201]

Percent Male Patients 1,562 44.126 (14.404) -0.0331 [-.127,.0609] -0.147 [-.242,-.052] -0.143 [-.241,-.0453]

Average HCC Risk Score for Commercial Patients 1,562 5.2737 (5.2598) 0.0613 [.032,.0906] - - - -

Average HCC Risk Score for Medicaid Patients 1,458 10.303 (7.5459) 0.00444 [-.0399,.0488] - - - -

Number of Patients for Face-to-Face Visits 1,562 584.64 (417.21) -5.69 [-7.85,-3.53] -5.56 [-8.16,-2.96] -6.12 [-8.79,-3.45]

Average Number of Visits per Patient for Commercial

Patients 1,562 2.3661 (.89263) -0.00561 [-.0109,-.0003

29] -0.00994 [-.0166,-.003

29] -0.011 [-.0179,-.004

11]

Average Number of Visits per Patient for Medicaid

Patients 1,459 2.4478 (1.1211) -0.00559 [-.0127,.0015] -0.00598

[-.0133,.0013

9] -0.00654

[-.0141,.0010 3]

Network Characteristics***

Eigenvector Centrality 1,211

.0040017

(.029747) -0.232 [-.299,-.165] -0.075 [-.13,-.0203] -0.0532

[-.101,-.0051 4]

Note: *Controls for average patient HCC score and physician 3-digit ZIP Code are included. **Controls for practicing in an academic medical center, average patient HCC score, and physician 3-digit ZIP Code are included. 43 observations are missing for practice location in an academic medical center, reducing the number of observations for some variables. ***Network characteristics are calculated for the Boston Hospital Referral Region only. Regression estimates are from a Poisson model with robust standard errors,

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therefore the interpretation of the coefficients is in % rather than levels.

Figure S1: Distribution of Percentage of Medicaid Patients for Surgical Specialists

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