Table 3.

F-Statistics Testing Whether Patient Groups Defined by Model Variables Are Related to the Use of For-Profit Dialysis Centers, 1996–1999

Variable Group (Degrees of Freedom)	Partial F-statistic* (p-Value)
Instrument
Differential distance (17, 101,554)	2,150.53 (<.0001)
Covariates
Gender (1, 101,554)	5.81 (.0159)
Age (1, 101,554)	7.29 (.0069)
Year (3, 101,554)	59.53 (<.0001)
Race (8, 101,554)	6.26 (<.0001)
Comorbidity (17, 101,554)	8.55 (<.0001)
Previous health care use (4, 101,554)	2.63 (.0326)
State (50, 101,554)	212.00 (<.0001)
Actual distance (4, 101,554)	75.41 (<.0001)
Patient zip code rural % (3, 101,554)	57.46 (<.0001)
Patient zip code poverty % (3, 101,554)	3.52 (.0144)
Patient zip code per capita income ($) (3, 101,554)	5.91 (.0005)

^*Against the null hypothesis that the groups defined by the instrumental variables do not describe a significant portion of treatment variation.