Supplementary Online Content

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1 Supplementary Online Content Valley TS, Sjoding MW, Ryan AM, Iwashyna TJ, Cooke CR. Association of intensive care unit admission with mortality among older patients with pneumonia. JAMA. doi: /jama etable 1. International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) codes efigure 1. Study selection criteria/recruitment table eappendix 1. Appendix on statistical methods for the instrumental variable analysis etable 2. Instrument analysis relationship between ICU admission and differential distance (condition #1) etable 3. Patient characteristics by median differential distance etable 4. Instrument analysis absence of relationship between 30-day mortality and differential distance (condition #2) etable 5. Instrument analysis absence of relationship between Medicare spending and differential distance (condition #2) etable 6. Instrument analysis absence of relationship between hospital costs and differential distance (condition #2) etable 7. Hospital characteristics by ICU admission quintiles efigure 2. Conceptual diagram of the marginal population identified by instrumental variable model eappendix 2. Inverse probability weighting etable 8. Elixhauser comorbidities by ICU admission etable 9. Instrumental variable analysis model results for 30-day mortality etable 10. Instrumental variable analysis model results for Medicare spending etable 11. Instrumental variable analysis model results for hospital costs etable 12. Instrumental variable analysis on costs per patient by in-hospital mortality ereferences This supplementary material has been provided by the authors to give readers additional information about their work.

2 etable 1. International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) Codes Diagnosis ICD-9-CM Codes Pneumonia , 480.8, 480.9, 481, 482.0, 482.1, 482.2, , , , , , 482.9, 483.0, 483.1, 483.8, 485, 486, Viral pneumonia , 480.8, 480.9, Bacterial pneumonia 481, 482.0, 482.1, 482.2, , , , , , 482.9, 483.0, 483.1, Acute respiratory failure , , , Sepsis 038.x, , , Shock 458, , 958.4, Respiratory or cardiac arrest 427.5, Procedures Mechanical ventilation 96.7, 96.70, 96.71, 96.72, Cardiopulmonary resuscitation 99.60, 99.63

3 efigure 1. Study selection criteria/recruitment table 1,327,370 Admissions to patients with eligible ICD-9- CM for pneumonia from 2010 to ,963 Excluded (8.2%) 47,488 Transferred in from another hospital (3.6%) 40,112 In hospitals without ICU capabilities (3.0%) 18,239 Missing geographic coordinates (1.6%) 124 Admissions to U.S. territories (0.01%) 1,221,407 Admissions met study inclusion criteria 109,013 Excluded as readmissions in the same year (9.0%) 1,112,394 Patients with a single hospitalization per year 328,404 ICU patients 783,990 Ward patients

4 eappendix 1. Appendix on statistical methods for the instrumental variable analysis The instrument for this study was differential distance, defined as the difference between 1) the distance between a patient s residence to the nearest high ICU use hospital and 2) the distance from a patient s residence to the nearest hospital of any type. For the instrument to be considered valid, it must meet three conditions. Conditions #1 and #2 can be demonstrated empirically. Condition #3 cannot be proven but can be evaluated. 1 Condition 1. The instrument must be associated with the treatment. In this study, differential distance must be associated with ICU admission. As demonstrated in etable 2, differential distance is highly correlated with ICU admission (Partial F (1, 2986) = 245), conditional on other covariates. A general rule of thumb is that an instrument is strong if it has an F-statistic > 10. 2,3 For every 10-mile increase in differential distance, the probability of ICU admission decreases by 1.5. When stratified by the median differential distance (3.3 miles), ICU admission was 36% in the lower half and 23% in the upper half. Condition 2. The instrument must not be associated with the outcome, except through the treatment. In this study, differential distance should not be associated with 30-day mortality, Medicare payments, or hospital costs, except through ICU admission. As demonstrated in etables 4-6, differential distance is not correlated with 30-day mortality (P value = 0.92), Medicare payments (P value = 0.21), or hospital costs (P value = 0.07), conditional on other covariates. Condition 3. There should be no mutual confounders between the instrument and the outcome. This condition cannot be proven. Instead, it can be evaluated by examining covariate balance as stratified by the instrument. In etable 3, patient characteristics are stratified by median differential distance. In etable 7, hospital characteristics are stratified by quintiles of ICU admission rate. Distance instruments are inherently linked to urbanicity (and other associated factors such as race and socioeconomic status). 4 Using differential distance instead of absolute distance attenuates this association but rarely prevents it. Although it is not clear if adjustment for or stratification by covariates with imbalance in the IV model eliminates bias, this is the recommended approach to covariates with any imbalance. 4 All models were adjusted for patient characteristics listed in Table 1 and hospital characteristics listed in Table 2. All 29 Elixhauser comorbidities were included in models individually. Angus organ failure score, 5 which identifies severity of illness by patient organ failures derived from the administrative record with a maximum score of six and higher scores indicating more organ failures, included all organ failures numbered 0 to > 5. Hospital region comprised the nine regions by U.S. census definitions. All models adjusted standard errors for clustering of patients within hospitals. Test of endogeneity To determine if the IV model estimating the relationship between ICU admission and the outcomes improves upon a standard model fit without the IV, the Durbin-Wu-Hausman test of endogeneity was performed for each outcome. Results for 30-day mortality (F statistic = 16.1, p<0.001), Medicare spending (F statistic = 14.2, p<0.001), and hospital costs (F statistic = 7.9, p<0.01) were each significant, indicating that the ordinary least-squares model results in biased estimations when compared to the instrumental variable analysis. 2

5 etable 2. Instrument analysis relationship between ICU admission and differential distance (condition #1) F-statistic (1, 2986) P value Adj. R- squared Beta 95% CI absolute change in ICU admission probability for every 10 mile increase in differential distance (-0.02, -0.01) 245 < Condition #1 Beta 95% Conf. Interval P value Differential distance per 10 miles , < Age years , < > 85 years , < Sex , < Race Black , Other , Admission Source Emergency department , Urbanicity Large Suburban Metropolitan , Medium Metropolitan , Small Metropolitan , Micropolitan , 0.04 < Noncore , < Median Income by Categories Median Income $40,000-$100, , Median Income > $100, , Angus Organ Failure Score , < , < , < , < > , < Elixhauser Comorbidities Congestive Heart Failure , < Valvular Disease , < Pulmonary Circulation Disorders , < Peripheral Vascular Disorders , < Hypertension , < Paralysis , < Other Neurological Disorders , < Chronic Pulmonary Disease , < Uncomplicated Diabetes , < Complicated Diabetes , < Hypothyroidism , < Renal Failure , Liver Disease , Peptic Ulcer Disease , AIDS , Lymphoma , 0.02 < Metastatic Cancer , Solid Tumor , Collagen Vascular Disease , < Coagulopathy , < Obesity , < Weight Loss , < Fluid and Electrolyte Disorders , < Blood Loss Anemia , < Deficiency Anemias , < Alcohol Abuse , < Drug Abuse , Psychoses , Depression , < Mechanical ventilation , < Cardiopulmonary resuscitation , Respiratory failure , < 0.001

6 Sepsis , 0.12 < Shock , 0.2 < Arrest , < Type of Pneumonia Viral Pneumonia , Bacterial Pneumonia , < Region Mid-Atlantic , South Atlantic , East North Central , East South Central , West North Central , West South Central , < Mountain , Pacific , Hospital Ownership Type For-profit , Government , Hospital Teaching Status (Ratio of Resident FTE to Hospital Beds) , < Hospital Size by Beds, per 100 Beds , ICU Size by Proportion of Hospital Beds 5-10% , > 10% , Proportion of Medicaid Patients Served, per Hospital Admission , Hospital Technology Index a < , Hospital Nursing Ratio, Nurse FTE per 1,000 Patient-Days , Hospital Annual Pneumonia Case Volume, per 100 Cases , < Year of Admission , < , < Constant , < a The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service. The beta for technology index represents change in one unit of the technology index per one unit change of the outcome.

7 etable 3. Patient characteristics by median differential distance Characteristics < 3.3 miles No. (%) > 3.3 miles No. (%) No. Patients a 553, ,797 ICU Admission 201,144 (36.3) 127,260 (22.8) Age, mean (SD) 80 (8) 80 (8) years 172,791 (31.2) 170,502 (30.5) years 195,113 (35.2) 202,474 (36.2) > 85 years 185,693 (33.5) 185,821 (33.3) Female 303,602 (54.8) 302,561 (54.2) Race/Ethnicity White 450,202 (81.3) 511,949 (91.6) Black 65,976 (11.9) 30,671 (5.5) Other 37,419 (6.8) 16,177 (2.9) Urbanicity Large Central Metropolitan 191,181 (34.6) 36,797 (6.6) Large Suburban Metropolitan 139,724 (25.3) 119,372 (21.4) Medium Metropolitan 113,734 (20.6) 126,148 (22.6) Small Metropolitan 42,604 (7.7) 92,341 (16.6) Micropolitan 36,842 (6.7) 108,219 (19.4) Noncore 28,503 (5.2) 74,499 (13.4) Median Household Income by Zip Code < $40, ,696 (25.1) 155,669 (27.9) $40,000-$100, ,111 (68.3) 375,613 (67.2) > $100,000 36,790 (6.7) 27,515 (4.9) Elixhauser Comorbidities Count, mean (SD) 2.6 (1.1) 2.7 (1.1) Congestive Heart Failure 158,167 (28.6) 162,766 (29.1) Valvular Disease 23,850 (4.3) 27,749 (5.0) Pulmonary Circulation Disorders 25,656 (4.6) 26,628 (4.8) Peripheral Vascular Disorders 24,270 (4.4) 26,322 (4.7) Hypertension 276,201 (49.9) 290,923 (52.1) Paralysis 17,309 (3.1) 13,854 (2.5) Other Neurological Disorders 32,813 (5.9) 35,068 (6.3) Chronic Pulmonary Disease 207,142 (37.4) 230,502 (41.3) Uncomplicated Diabetes 102,038 (18.4) 108,859 (19.5) Complicated Diabetes 13,060 (2.4) 13,375 (2.4) Hypothyroidism 56,703 (10.2) 64,546(11.6) Renal Failure 88,570 (16.0) 89,731 (16.1) Liver Disease 4,966 (0.9) 4,375 (0.8) Peptic Ulcer Disease 94 (0.02) 87 (0.02) AIDS 413 (0.1) 136 (0.02) Lymphoma 11,249 (2.0) 11,002 (2.0) Metastatic Cancer 20,997 (3.8) 19,295 (3.5) Solid Tumor 22,938 (4.1) 22,808 (4.1) Collagen Vascular Disease 14,322 (2.6) 16,744 (3.0) Coagulopathy 26,581 (4.8) 23,411 (4.2) Obesity 15,935 (2.9) 17,498 (3.1) Weight Loss 56,937 (10.3) 48,985 (8.8) Fluid and Electrolyte Disorders 208,112 (37.6) 199,601 (35.7) Blood Loss Anemia 2,062 (0.4) 2,578 (0.5) Deficiency Anemias 84,063 (15.2) 89,448 (16.0) Alcohol Abuse 1,231 (0.2) 1,375 (0.3) Drug Abuse 442 (0.1) 425 (0.1) Psychoses 11,448 (2.1) 11,446 (2.1) Depression 29,479 (5.3) 36,332 (6.5)

8 Admission Source Outpatient 429,586 (77.6) 439,961 (78.7) Emergency Department 121,857 (22.0) 117,037 (20.9) Hospital Diagnoses Pneumonia as Primary Diagnosis 353,378 (63.8) 401,174 (71.8) Respiratory Failure 190,355 (34.4) 157,614 (28.2) Sepsis 137,583 (24.9) 108,498 (19.4) Shock 63,005 (11.4) 36,712 (6.6) Cardiac or Respiratory Arrest 6,659 (1.2) 4,663 (0.8) Type of Pneumonia Unspecified Pneumonia 479,638 (86.6) 483,295 (86.5) Viral Pneumonia 5,778 (1.0) 5,474 (1.0) Bacterial Pneumonia 68,181 (12.3) 70,028 (12.5) Procedures Performed during Hospitalization Mechanical Ventilation 109,635 (19.8) 72,236 (12.9) Cardiopulmonary Resuscitation 6,975 (1.3) 4,097 (0.7) Angus Organ Failure Score b 0 329,346 (59.5) 376,960 (67.5) 1 136,563 (24.7) 125,685 (22.5) > 2 87,688 (15.8) 56,152 (10.1) Year of Admission ,628 (48.5) 189,737 (51.5) ,431 (50.7) 189,082 (49.3) ,538 (50.1) 179,978 (49.9) Outcomes < 3.3 miles No. (%) > 3.3 miles No. (%) No. Patients 553, ,797 Length of Stay in Days, median (IQR) c 5 (3-8) 4 (3-7) Quartiles of Total Medicare Payment per Patient 1 ($0-$4,981) 118,840 (21.5) 159,453 (28.5) 2 ($4,982-$7,639) 128,207 (23.2) 149,776 (26.8) 3 ($7,640-$11,162) 137,196 (24.8) 140,879 (25.2) 4 ($11,163-$882,637) 169,354 (30.6) 108,689 (19.5) Quartiles of Hospital Costs per Patient 1 ($153-$4,614) 124,569 (22.6) 152,278 (27.3) 2 ($4,615-$7,389) 127,354 (23.1) 149,540 (26.9) 3 ($7,390-$13,154) 136,440 (24.8) 140,445 (25.2) 4 ($13,155-$1,375,266) 162,127 (29.5) 114,764 (20.6) Discharge Destination Home 271,652 (49.2) 299,801 (54.2) Rehabilitation or Nursing Facility 173,853 (31.5) 166,097 (30.0) Dead 64,508 (11.7) 50,583 (9.1) Other 41,997 (7.6) 36,909 (6.7) 30-Day Readmission 97,188 (17.6) 96,774 (17.3) 30-Day Mortality 113,578 (20.5) 96,482 (17.3) a 11,703 (1%) of patients were excluded from regression models due to missing differential distance (n=5,166), admission source (n=4,053), urban/rural (n=2,430), pneumonia volume (n=107) b Measures severity of illness by patient organ failures from the billing record with a high score of six and higher scores indicating more failures c Interquartile range

9 etable 4. Instrument analysis absence of relationship between 30-day mortality and differential distance (condition #2) Beta 95% CI F-statistic (1, 2986) P value absolute increase in 30-day mortality for every 10 mile increase in differential distance ( , ) Condition #2 Beta 95% Conf. Interval P value Differential distance per 10 miles , Age years , < > 85 years , < Sex , < Race Black , < Other , < Admission Source Emergency department , < Urbanicity Large Suburban Metropolitan , Medium Metropolitan , Small Metropolitan , Micropolitan , < Noncore , < Median Income by Categories Median Income $40,000-$100, , Median Income > $100, , Angus Organ Failure Score , < , < , < , < > , 0.34 < Elixhauser Comorbidities Congestive Heart Failure , < Valvular Disease , < Pulmonary Circulation Disorders , < Peripheral Vascular Disorders , 0.01 < Hypertension , < Paralysis , < Other Neurological Disorders , < Chronic Pulmonary Disease , < Uncomplicated Diabetes , < Complicated Diabetes , < Hypothyroidism , < Renal Failure , < Liver Disease , < Peptic Ulcer Disease , AIDS , Lymphoma , < Metastatic Cancer , < Solid Tumor , 0.14 < Collagen Vascular Disease , < Coagulopathy , < Obesity , < Weight Loss , < Fluid and Electrolyte Disorders , < Blood Loss Anemia , < Deficiency Anemias , < Alcohol Abuse , Drug Abuse , < Psychoses , < Depression , < Mechanical ventilation , < Cardiopulmonary resuscitation , < Respiratory failure , 0.15 < 0.001

10 Sepsis , < Shock , < Arrest , < Type of Pneumonia Viral Pneumonia , < Bacterial Pneumonia , < Region Mid-Atlantic , South Atlantic , < East North Central , East South Central , < West North Central , West South Central , < Mountain , Pacific , Hospital Ownership Type For-profit , Government , Hospital Teaching Status (Ratio of Resident FTE to Hospital Beds) , Hospital Size by Beds, per 100 Beds , ICU Size by Proportion of Hospital Beds 5-10% , > 10% , Proportion of Medicaid Patients Served, per Hospital Admission , Hospital Technology Index a , Hospital Nursing Ratio, Nurse FTE per 1,000 Patient-Days , < Hospital Annual Pneumonia Case Volume, per 100 Cases , < Year of Admission , 0.01 < , Constant , < a The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service. The beta for technology index represents change in one unit of the technology index per one unit change of the outcome.

11 etable 5. Instrument analysis absence of relationship between Medicare spending and differential distance (condition #2) Beta 95% CI F-statistic (1, 2986) P value $19.6 per 10 mile increase in differential distance (-11, 25) Condition #2 Beta 95% Conf. Interval P value Differential distance per 10 miles , Age years , < > 85 years , < Sex , < Race Black , < Other , < Admission Source Emergency department , Urbanicity Large Suburban Metropolitan , < Medium Metropolitan , < Small Metropolitan , < Micropolitan , < Noncore , < Median Income by Categories Median Income $40,000-$100, , Median Income > $100, , Angus Organ Failure Score , < , < , < , < > , < Elixhauser Comorbidities Congestive Heart Failure , < Valvular Disease , < Pulmonary Circulation Disorders , < Peripheral Vascular Disorders , < Hypertension , < Paralysis , < Other Neurological Disorders , < Chronic Pulmonary Disease , < Uncomplicated Diabetes , -707 < Complicated Diabetes , < Hypothyroidism , -453 < Renal Failure , < Liver Disease , Peptic Ulcer Disease , AIDS , < Lymphoma , Metastatic Cancer , < Solid Tumor , Collagen Vascular Disease , < Coagulopathy , < Obesity , < Weight Loss , < Fluid and Electrolyte Disorders , < Blood Loss Anemia , < Deficiency Anemias , < Alcohol Abuse , Drug Abuse , < Psychoses , < Depression , < Mechanical ventilation , < Cardiopulmonary resuscitation , < Respiratory failure , < Sepsis , 3434 < 0.001

12 Shock , < Arrest , < Type of Pneumonia Viral Pneumonia , Bacterial Pneumonia , < Region Mid-Atlantic , South Atlantic , < East North Central , < East South Central , < West North Central , < West South Central , < Mountain , < Pacific , < Hospital Ownership Type For-profit , Government , Hospital Teaching Status (Ratio of Resident FTE to Hospital Beds) , < Hospital Size by Beds, per 100 Beds 58-30, ICU Size by Proportion of Hospital Beds 5-10% , > 10% , Proportion of Medicaid Patients Served, per Hospital Admission , < Hospital Technology Index a , Hospital Nursing Ratio, Nurse FTE per 1,000 Patient-Days , Hospital Annual Pneumonia Case Volume, per 100 Cases , Year of Admission , , Constant , < a The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service. The beta for technology index represents change in one unit of the technology index per one unit change of the outcome.

13 etable 6. Instrument analysis absence of relationship between hospital costs and differential distance (condition #2) Beta 95% CI F-statistic (1, 2940) P value -$42 per 10 mile increase in differential distance (-87, 3) Condition #2 Beta 95% Conf. Interval P value Differential distance per 10 miles , Age years , < > 85 years , < Sex , < Race Black , < Other , < Admission Source Emergency department , < Urbanicity Large Suburban Metropolitan , Medium Metropolitan , < Small Metropolitan , < Micropolitan , < Noncore , < Median Income by Categories Median Income $40,000-$100, , < Median Income > $100, , < Angus Organ Failure Score , < , < , < , < > , < Elixhauser Comorbidities Congestive Heart Failure , < Valvular Disease , < Pulmonary Circulation Disorders , < Peripheral Vascular Disorders , < Hypertension , < Paralysis , < Other Neurological Disorders , < Chronic Pulmonary Disease , < Uncomplicated Diabetes , < Complicated Diabetes , < Hypothyroidism , < Renal Failure , < Liver Disease , Peptic Ulcer Disease , AIDS , Lymphoma , < Metastatic Cancer , -410 < Solid Tumor , Collagen Vascular Disease , < Coagulopathy , -872 < Obesity , < Weight Loss , < Fluid and Electrolyte Disorders , Blood Loss Anemia , < Deficiency Anemias , < Alcohol Abuse , Drug Abuse , Psychoses , < Depression , < Mechanical ventilation , < Cardiopulmonary resuscitation , < Respiratory failure , < Sepsis , 673 < 0.001

14 Shock , < Arrest , Type of Pneumonia Viral Pneumonia , < Bacterial Pneumonia , < Region Mid-Atlantic , South Atlantic , < East North Central , East South Central , < West North Central , West South Central , < Mountain , Pacific , < Hospital Ownership Type For-profit , Government , Hospital Teaching Status (Ratio of Resident FTE to Hospital Beds) , Hospital Size by Beds, per 100 Beds , ICU Size by Proportion of Hospital Beds 5-10% , > 10% , Proportion of Medicaid Patients Served, per Hospital Admission , Hospital Technology Index a , Hospital Nursing Ratio, Nurse FTE per 1,000 Patient-Days , < Hospital Annual Pneumonia Case Volume, per 100 Cases , Year of Admission , , Constant , < a The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service. The beta for technology index represents change in one unit of the technology index per one unit change of the outcome.

15 etable 7. Hospital characteristics by ICU admission quintiles Quintile 1 (<19%) No. (%) Quintile 2 (19-25%) No. (%) Quintile 3 (26-32%) No. (%) Quintile 4 (33-44%) No. (%) Quintile 5 (>44%) No. (%) Characteristics No. Hospitals Hospital Ownership For-profit 85 (14.4) 107 (17.6) 126 (21.2) 160 (26.7) 201 (33.9) Not-for-profit 413 (69.9) 419 (68.8) 377 (63.4) 345 (57.5) 316 (53.3) Government 93 (15.7) 83 (13.6) 92 (15.5) 95 (15.8) 76 (12.8) Medical School Affiliation 176 (29.8) 175 (28.7) 194 (32.6) 235 (39.2) 218 (36.8) Teaching Status No Residents 483 (81.7) 486 (79.8) 479 (80.5) 447 (74.5) 444 (74.9) Minor Teaching Program (< 0.25 residents/bed) 86 (14.6) 87 (14.3) 84 (14.1) 102 (17.0) 100 (16.9) Major Teaching Program (> 0.25 residents/bed) 22 (3.7) 36 (5.9) 32 (5.4) 51 (8.5) 49 (8.3) Hospital Beds < (42.6) 169 (27.8) 147 (24.7) 120 (20.0) 80 (13.5) (27.4) 184 (30.2) 181 (30.4) 183 (30.5) 190 (32.0) > (29.9) 256 (42.0) 267 (44.9) 297 (49.5) 323 (54.5) Percent of ICU Beds < 5% 93 (15.7) 67 (11.0) 79 (13.3) 69 (11.5) 97 (16.4) 5-10% 298 (50.4) 318 (52.2) 266 (44.7) 245 (40.8) 216 (36.4) > 10% 200 (33.8) 224 (36.8) 250 (42.0) 286 (47.7) 280 (47.2) Hospital Pneumonia Annual Case Volume, Mean (SD) 406 (363) 496 (352) 434 (321) 410 (320) 308 (240) Nursing FTE a per 1000 Patient-Days, Mean (SD) 3.7 (1.7) 3.8 (1.4) 3.8 (1.3) 4.0 (1.6) 4.0 (1.4) Technology Index b, Mean (SD) 19.6 (11.9) 21.9 (12.3) 21.2 (12.9) 22.9 (14.6) 20.9 (14.4) Medicaid Patients < 7% 293 (49.6) 234 (38.4) 207 (34.8) 170 (28.3) 100 (16.9) 7-11% 215 (36.4) 219 (36.0) 234 (39.3) 202 (33.7) 204 (34.4) > 11% 83 (14.0) 156 (25.6) 154 (25.9) 228 (38.0) 289 (48.7) Census Regions Northeast 127 (21.5) 127 (20.9) 92 (5.5) 80 (13.3) 68 (11.5) Midwest 188 (31.8) 200 (32.8) 208 (35.0) 226 (37.7) 212 (35.8) South 188 (31.8) 187 (30.7) 194 (32.6) 168 (28.0) 151 (25.5) West 88 (14.9) 95 (15.6) 101 (17.0) 126 (21.0) 162 (27.3) a Full-time equivalents b The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service.

16 efigure 2. Conceptual diagram of the marginal population identified by instrumental variable model Example #1: Low-ICU use hospital (a) Never admitted to ICU (b1) Not admitted to ICU (marginal untreated) (c) Always admitted to ICU ICU Admission Threshold Example #2: High-ICU use hospital (a) Never admitted to ICU (b2) Admitted to ICU (marginal treated) (c) Always admitted to ICU ICU Admission Threshold In example #1, the hospital uses the ICU less and has a higher threshold for ICU admission while in example #2, the hospital uses the ICU more frequently and has a lower threshold for ICU admission. In both hospitals, there will be a population of patients who would never be admitted to the ICU (group a ) as well as patients who would always be admitted to the ICU (group c ). At the same time, there will be a group of patients who would either not be admitted (group b1 ) or would be admitted (group b2 ) to the ICU solely because of the hospital to which they presented. These b groups together are the marginal population. In the instrumental variable analysis, differential distance attempts to replicate random assignment of patients as patients living closer to a high-icu use hospital would be more likely to be admitted to this hospital, which would increase their probability of being admitted to the ICU.

17 eappendix 2. Inverse probability weighting To assess the robustness of the results to the choice of modeling method, the average treatment effect of ICU admission on 30-day mortality was determined using inverse probability weighting (IPW). Inverse probability weighting IPW is a technique that attempts to estimate what one cannot observe - the effect of ICU admission compared to withholding ICU admission in the same individual. 6 It relies on the assumption that all individuals could conceivably be cared for in either ICU or non-icu setting. Practically, the technique involves weighting observations by the inverse of a function of their probability of ICU admission, and then performing weighted regression. Conceptually, to estimate the IPW estimate, the propensity score was first generated, the probability of ICU admission was determined using a logistic regression model including observed patient and hospital covariates. After evaluating covariate balance and propensity score distribution overlap across ICU admission status, weights for each patient were generated. Weights for patients admitted to the ICU were calculated as the reciprocal of their probability of ICU admission. Weights for patients who were not admitted to the ICU were calculated as the reciprocal of one minus the probability of ICU admission. Thus, exposed individuals who have a high probability of exposure are weighted less than those who have a small probability of exposure. Finally, a weighted linear regression was performed to estimate the effect of ICU admission on 30-day mortality. The preceding sequence of steps was implemented in Stata s teffects command.

18 etable 8. Elixhauser comorbidities by ICU admission ICU Patients No. (%) Ward Patients No. (%) No. Patients 328, ,990 Congestive Heart Failure 122,197 (37.2) 198,736 (25.4) Valvular Disease 11,810 (3.6) 39,789 (5.1) Pulmonary Circulation Disorders 19,387 (5.9) 32,897 (4.2) Peripheral Vascular Disorders 11,782 (3.6) 38,810 (5.0) Hypertension 110,209 (33.6) 456,915 (58.3) Paralysis 11,499 (3.5) 19,664 (2.5) Other Neurological Disorders 14,440 (4.4) 53,441 (6.8) Chronic Pulmonary Disease 118,865 (36.2) 318,779 (40.7) Uncomplicated Diabetes 44,722 (13.6) 166,175 (21.2) Complicated Diabetes 5,971 (1.8) 20,464 (2.6) Hypothyroidism 17,587 (5.4) 103,662 (13.2) Renal Failure 49,901 (15.2) 128,400 (16.4) Liver Disease 2,374 (0.7) 6,967 (0.9) Peptic Ulcer Disease 64 (0.02) 117 (0.01) AIDS 201 (0.1) 348 (0.04) Lymphoma 6,776 (2.1) 15,475 (2.0) Metastatic Cancer 13,024 (4.0) 27,268 (3.5) Solid Tumor 13,825 (4.2) 31,921 (4.1) Collagen Vascular Disease 5,320 (1.6) 25,746 (3.3) Coagulopathy 21,137 (6.4) 28,855 (3.7) Obesity 8,090 (2.5) 25,343 (3.2) Weight Loss 47,504 (14.5) 58,418 (7.5) Fluid and Electrolyte Disorders 143,603 (43.7) 264,110 (33.7) Blood Loss Anemia 1,150 (0.4) 3,490 (0.5) Deficiency Anemias 31,810 (9.7) 141,701 (18.1) Alcohol Abuse 876 (0.3) 1,730 (0.2) Drug Abuse 272 (0.1) 595 (0.1) Psychoses 5,139 (1.6) (2.3) Depression 8,435 (2.6) 57,376 (7.3)

19 etable 9. Instrument variable analysis model results for 30-day mortality R-squared for model = Day Mortality Beta 95% Conf. Interval P value ICU , Age years , < > 85 years , < Sex , < Race Black , < Other , < Admission Source Emergency department , < Urbanicity Large Suburban Metropolitan , Medium Metropolitan , Small Metropolitan , Micropolitan , < Noncore , < Median Income by Categories Median Income $40,000-$100, , Median Income > $100, , Angus Organ Failure Score , < , < , < , < > , 0.34 < Elixhauser Comorbidities Congestive Heart Failure , < Valvular Disease , < Pulmonary Circulation Disorders , < Peripheral Vascular Disorders , 0.01 < Hypertension , < Paralysis , < Other Neurological Disorders , < Chronic Pulmonary Disease , < Uncomplicated Diabetes , < Complicated Diabetes , < Hypothyroidism , < Renal Failure , < Liver Disease , < Peptic Ulcer Disease , AIDS , Lymphoma , < Metastatic Cancer , < Solid Tumor , 0.14 < Collagen Vascular Disease , < Coagulopathy , < Obesity , < Weight Loss , < Fluid and Electrolyte Disorders , < Blood Loss Anemia , < Deficiency Anemias , < Alcohol Abuse , Drug Abuse , < Psychoses , < Depression , < Mechanical ventilation , < Cardiopulmonary resuscitation , < Respiratory failure , 0.15 < Sepsis , < Shock , < 0.001

20 30-Day Mortality Beta 95% Conf. Interval P value Arrest , < Type of Pneumonia Viral Pneumonia , < Bacterial Pneumonia , < Region Mid-Atlantic , South Atlantic , < East North Central , East South Central , < West North Central , West South Central , < Mountain , Pacific , Hospital Ownership Type For-profit , Government , Hospital Teaching Status (Ratio of Resident FTE to Hospital Beds) , Hospital Size by Beds, per 100 Beds , ICU Size by Proportion of Hospital Beds 5-10% , > 10% , Proportion of Medicaid Patients Served, per Hospital Admission , Hospital Technology Index a , Hospital Nursing Ratio, Nurse FTE per 1,000 Patient-Days , < Hospital Annual Pneumonia Case Volume, per 100 Cases , < Year of Admission , 0.01 < , Constant , < a The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service. The beta for technology index represents change in one unit of the technology index per one unit change of the outcome.

21 etable 10. Instrument variable analysis model results for Medicare spending R-squared for model = 0.34 Medicare Spending Beta 95% Conf. Interval P value ICU , Age years , < > 85 years , < Sex , < Race Black , 1590 < Other , < Admission Source Emergency department , Urbanicity Large Suburban Metropolitan , < Medium Metropolitan , < Small Metropolitan , < Micropolitan , < Noncore , < Median Income by Categories Median Income $40,000-$100, , Median Income > $100, , Angus Organ Failure Score , < , < , < , < > , < Elixhauser Comorbidities Congestive Heart Failure , < Valvular Disease , < Pulmonary Circulation Disorders , < Peripheral Vascular Disorders , < Hypertension , < Paralysis , < Other Neurological Disorders , < Chronic Pulmonary Disease , < Uncomplicated Diabetes , < Complicated Diabetes , < Hypothyroidism , -459 < Renal Failure , < Liver Disease , Peptic Ulcer Disease , AIDS , < Lymphoma , Metastatic Cancer , < Solid Tumor , Collagen Vascular Disease , < Coagulopathy , < Obesity , < Weight Loss , < Fluid and Electrolyte Disorders , < Blood Loss Anemia , < Deficiency Anemias , < Alcohol Abuse , Drug Abuse , < Psychoses , < Depression , < Mechanical ventilation , < Cardiopulmonary resuscitation , < Respiratory failure , < Sepsis , < Shock ,

22 Medicare Spending Beta 95% Conf. Interval P value Arrest , < Type of Pneumonia Viral Pneumonia , Bacterial Pneumonia , < Region Mid-Atlantic , South Atlantic , < East North Central , < East South Central , < West North Central , < West South Central , < Mountain , < Pacific , < Hospital Ownership Type For-profit , Government , Hospital Teaching Status (Ratio of Resident FTE to Hospital Beds) , < Hospital Size by Beds, per 100 Beds 64-28, ICU Size by Proportion of Hospital Beds 5-10% , > 10% , Proportion of Medicaid Patients Served, per Hospital Admission , < Hospital Technology Index a , Hospital Nursing Ratio, Nurse FTE per 1,000 Patient-Days , Hospital Annual Pneumonia Case Volume, per 100 Cases 9-149, Year of Admission , , Constant , < a The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service. The beta for technology index represents change in one unit of the technology index per one unit change of the outcome.

23 etable 11. Instrument variable analysis model results for hospital costs R-squared for model = 0.32 Hospital Costs Beta 95% Conf. Interval P value ICU , Age years , -931 < > 85 years , < Sex , < Race Black , < Other , < Admission Source Emergency department , < Urbanicity Large Suburban Metropolitan , Medium Metropolitan , < Small Metropolitan , < Micropolitan , < Noncore , < Median Income by Categories Median Income $40,000-$100, , < Median Income > $100, , < Angus Organ Failure Score , < , < , < , < > , < Elixhauser Comorbidities Congestive Heart Failure , < Valvular Disease , < Pulmonary Circulation Disorders , < Peripheral Vascular Disorders , 396 < Hypertension , < Paralysis , < Other Neurological Disorders , < Chronic Pulmonary Disease , < Uncomplicated Diabetes , < Complicated Diabetes , < Hypothyroidism , < Renal Failure , 876 < Liver Disease , Peptic Ulcer Disease , AIDS , Lymphoma , < Metastatic Cancer , -425 < Solid Tumor , Collagen Vascular Disease , < Coagulopathy , < Obesity , < Weight Loss , < Fluid and Electrolyte Disorders , Blood Loss Anemia , < Deficiency Anemias , < Alcohol Abuse , Drug Abuse , Psychoses , < Depression , < Mechanical ventilation , < Cardiopulmonary resuscitation , < Respiratory failure , < Sepsis , Shock , < 0.001

24 Hospital Costs Beta 95% Conf. Interval P value Arrest , Type of Pneumonia Viral Pneumonia , < Bacterial Pneumonia , < Region Mid-Atlantic , South Atlantic , -700 < East North Central , East South Central , < West North Central , West South Central , < Mountain , Pacific , < Hospital Ownership Type For-profit , Government , Hospital Teaching Status (Ratio of Resident FTE to Hospital Beds) , Hospital Size by Beds, per 100 Beds 71-31, ICU Size by Proportion of Hospital Beds 5-10% , > 10% , Proportion of Medicaid Patients Served, per Hospital Admission , Hospital Technology Index a 5-9.2, Hospital Nursing Ratio, Nurse FTE per 1,000 Patient-Days , < Hospital Annual Pneumonia Case Volume, per 100 Cases , Year of Admission , , Constant , < a The technology index is a weighted sum of the following hospital capabilities: obstetrics, medical/surgical intensive care unit, cardiac intensive care unit, emergency department, trauma center, open heart surgery, radiation therapy, computed tomography, diagnostic radiology, magnetic resonance imaging, positron-emission tomography, single-photon emission computed tomography, ultrasonography, and transplantation service. The beta for technology index represents change in one unit of the technology index per one unit change of the outcome.

25 etable 12. Instrumental variable analysis on costs per patient by in-hospital mortality Instrumental Variable Adjusted Medicare Payments per Patient Stratified by Survival Model a ICU Ward Absolute difference (95% CI) P value Patients Patients Surviving Patients $8,736 $10,165 -$1,429 (-3294, 436) 0.13 Deceased Patients $20,534 $18,359 $2,175 (-3302, 7651) 0.44 Instrumental Variable Adjusted Hospital Costs per Patient Stratified by Survival Model a ICU Ward Absolute difference (95% CI) P value Patients Patients Surviving Patients $13,057 $10,653 $2,404 (-395, 5204) 0.09 Deceased Patients $22,013 $15,531 $6,482 (-784, 13748) 0.08 a 2-stage least squared regression of all patients using differential distance to nearest high-icu use hospital as instrumental variable, adjusted for all variables in tables 1 and 2. All 29 Elixhauser comorbidities were included in models individually. Angus organ failure score, which identifies severity of illness by patient organ failures derived from the administrative record with a maximum score of six (higher scores indicate more organ failures), was defined to include all organ failures numbered 0 to > 5. Hospital region included the nine regions by U.S. census definitions. All models included clustering of patients within hospitals.

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