Table 1.

Patient-level baseline characteristics by zip code category

CharacteristicsProportion of Black Residents in Zip CodeP
<5%5 to 14.9%15 to 24.9%25 to 49.9%>50%
Total number of patients (n)41,12617,257817011,44314,004
    Number of white patients39,01312,839450138141378
    Number of black patients211344183669762912,626
Black patients (%)5.1425.6044.9166.6790.16<0.001
Mean age (years)66.4763.9861.8860.8759.61<0.001
Gender (% women)41.7043.4145.9148.0350.64<0.001
Employed at form completion (%)12.0112.5612.6810.7810.98<0.001
Health insurance at onset of ESRD (%)
    Veterans Affairs1.821.941.761.711.540.11
    Employee group coverage31.1931.431.4627.2726.58<0.001
    No coverage3.756.167.819.811.52<0.001
Comorbid conditions (%)
    Cardiac disease54.2450.6948.2944.8341.77<0.001
    Peripheral vascular disease17.7815.1715.3413.6410.08<0.001
Timing of nephrology referral (%)
    Not referred before RRT29.4731.9533.5736.4940.66
    <6 months before RRT12.8312.311.249.8111.34
    6 to 12 months before RRT27.9628.0127.9327.9627.01
    >12 months before RRT29.7427.7527.2625.7420.99<0.001
  • The first three lines provide number of patients in each zip code and race category for reference. P values for categorical variables were calculated using χ2 tests and those for continuous variables were calculated using the Kruskal-Wallis test. No characteristic had missing values.