Table 3.

Surgeon and patient contributions to variance in use of partial nephrectomy and laparoscopy (1997–2002)

	1997–2002 (All patients)		2000–2002 (Tumor size ≤ 4 cm)
	Partial Nephrectomy	Laparoscopy†	Partial Nephrectomy
Characteristic
Number of patients	3,995	3,565	1,364
Number of urologists	1,487	1,426	820
Proportion of variance attributable to surgeon (residual intraclass correlation coefficient)‡	18.1%	37.4%	21.6%
Partitioned variances§
Unmeasured surgeon factors	17.5%	37.5%	21.7%
Surgeon nephrectomy case-  volume	4.5%	13.9%	6.4%
Patient demographics	7.4%	20.7%	9.4%
Comorbidity	4.7%	13.4%	6.7%
Tumor size	19.6%	14.6%	—

^†The multilevel model for use of laparoscopy was based on the sub sample of patients treated with radical nephrectomy

^‡This row presents percentage of variance attributable to the surgeon after adjusting for patient and tumor characteristics, as well as surgeon nephrectomy case-volume (the residual intraclass correlation coefficient). The denominator for calculation of this proportion includes the residual variance attributable to the surgeon random effect (after adjustment for patient demographics, comorbidity, tumor size, and surgeon case-volume), and the variance attributable to unmeasured patient or tumor variables plus error (see Appendix 4; Model 4.2 and Equation 4.1).

^§The denominator for the calculation of partitioned-variance proportions is the total variance (see Appendix 4; Models 4.3-4.7, Equations 4.2 and 4.3). The total variance includes three components: (1) the variance attributable to the surgeon (after adjustment for the corresponding fixed-effect covariate(s) in a given model); (2) the variance attributable to the corresponding measured covariate(s) (i.e., the fixed effects); and (3) the variance attributable to unmeasured patient or tumor variables plus error (see Appendix 4; Equation 4.3). The partitioned variance attributable to the surgeon is estimated using an “unconditional” model, which includes a surgeon-level random-effects term as the only independent variable; accordingly, the denominator for calculation of this percentage includes only two components: (1) the variance attributable to the surgeon, unadjusted for any other covariates, and (2) the variance attributable to unmeasured patient or tumor variables plus error (see Appendix 4; Equation 4.2).