Table 1.

Baseline characteristics by visit frequency

CharacteristicsAll n (%)Exposure Variable (Mean Number of Monthly Visits to Incident Patients During Run-In)Instrumental Variable (Mean Number of Monthly Visits to Prevalent Patients)
<4≥4Absolute Difference<3.7≥3.7Absolute Difference
All130,892 (100)
Age (years)
 20–4411,566 (8.8)9.38.50.88.98.80.1
 45–6437,535 (28.7)29.328.31.029.028.40.6
 65–7438,708 (29.6)29.429.7−0.329.629.60.0
 ≥7543,083 (32.9)32.033.5−1.532.633.3−0.7
Women61,038 (46.6)46.446.8−0.446.846.50.3
Race
 white84,723 (64.7)65.964.01.965.264.21.0
 African-American40,273 (30.8)28.832.1−3.329.632.0−2.4
 other5896 (4.5)5.34.01.35.13.81.3
 Hispanic14,838 (11.3)11.511.30.211.411.30.1
Primary cause of ESRD
 diabetes63,484 (48.5)47.948.9−1.048.448.6−0.2
 hypertension40,607 (31.0)30.931.1−0.231.131.00.1
 glomerulonephritis7514 (5.7)5.95.60.35.75.70.0
 other19,287 (14.7)15.314.40.914.814.70.1
 dual eligibilitya51,569 (39.4)39.339.5−0.239.239.6−0.4
Comorbidity score
 ≤450,248 (38.4)40.936.74.239.037.80.02
 >4 to ≤840,975 (31.3)31.031.5−0.531.031.7−0.01
 ≥839,669 (30.3)28.131.8−3.730.130.6−0.01
Comorbid conditions
 ASHD65,170 (49.8)47.851.1−3.349.550.1−0.6
 CHF72,212 (55.2)53.356.4−3.154.955.4−0.5
 CVA/TIA26,704 (20.4)19.421.1−1.720.320.5−0.2
 PVD48,663 (37.2)35.338.5−3.236.537.9−1.4
 Other cardiac41,098 (31.4)30.232.2−2.031.631.20.4
 COPD29,697 (22.7)21.823.3−1.522.822.60.2
 GI bleeding9575 (7.3)6.97.6−0.77.37.4−0.1
 Liver disease11,209 (8.6)7.59.3−1.87.79.5−1.8
 Dysrhythmia36,722 (28.1)26.928.8−1.928.327.80.5
 Cancer15,161 (11.6)11.111.9−0.811.311.9−0.7
 Diabetes89,481 (68.4)67.469.0−1.668.368.50.2
SES principle component < medianb63,001 (48.1)49.047.51.549.047.31.7
Urban93,012 (71.1)67.673.4−5.869.672.6−3.0
Dialysis sessions during run-in
 <3827,354 (20.9)27.316.710.621.520.31.2
 ≥38 to <3914,419 (11.0)11.610.61.011.011.1−0.1
 ≥3989,119 (68.1)61.272.7−11.567.568.7−1.2
Hospital days during run-in
 088,885 (67.9)72.065.26.867.568.3−0.8
 >0 to <821,164 (16.2)14.917.0−2.116.316.10.2
 ≥820,843(16.0)13.117.8−4.716.215.60.6
Estimated GFR (ml/min per 1.73 m2)
 <1069,641 (53.2)52.853.5−0.752.354.2−1.9
 10 to <1540,884 (31.2)31.431.10.331.630.80.8
  ≥1518,787 (14.4)14.614.20.414.813.90.9
 Missing1580 (1.2)1.21.20.01.31.10.2
Hemoglobin (g/dl)
 <1186,461 (66.1)66.066.10.166.365.90.4
  ≥11.035,354 (27.0)26.727.2−0.526.627.6−1.0
 Missing9077 (6.9)7.46.70.37.26.70.5
Serum albumin (g/dl)
 <3.459,174 (45.2)44.645.6−1.044.945.6−0.7
  ≥3.439,768 (30.4)30.030.6−0.629.531.3−1.8
 Missing31,950 (24.4)25.423.81.625.723.12.6
BMI (kg/m2)
 <18.54912 (3.8)3.83.70.13.83.70.1
 18.5 to <2542,962 (32.8)33.132.60.532.932.80.1
  ≥2581,402 (62.2)61.962.4−0.562.162.3−0.2
 Missing1616 (1.2)1.21.30.11.31.20.1
  • Unless otherwise indicated, all data are expressed as percentages. ASHD, atherosclerotic heart disease; CHF, congestive heart failure; CVA/TIA, cerebrovascular accident/transient ischemic attack; PVD, peripheral vascular disease; COPD, chronic obstructive pulmonary disease; GI, gastrointestinal; SES, socioeconomic status; BMI, body mass index.

  • a Medicare and Medicaid.

  • b SES groups based on first principle component.