One-compartment model Two-compartment model Three-compartment model
Parameters XlSimEst*# WinNonlin ADAPT II* XlSimEst*# WinNonlin ADAPT II* XlSimEst*# WinNonlin ADAPT II*
K10 0.0079 ± 0.0011 0.0079 ± 0.0011 0.0079 ± 0.0011 0.0071 ± 0.0004 0.0071 ± 0.0004 0.0071 ± 0.0004 0.0067 ± 0.0010 0.0067 ± 0.0009 0.0067 ± 0.0009
K12       0.0218 ± 0.0021 0.0219 ± 0.0021 0.0219 ± 0.0021 0.0194 ± 0.0061 0.0195 ± 0.0063 0.0196 ± 0.0062
K21       0.0222 ± 0.0028 0.0222 ± 0.0028 0.0222 ± 0.0028 0.0632 ± 0.0436 0.0632 ± 0.0457 0.0635 ± 0.0457
K13             0.0121 ± 0.0073 0.0121 ± 0.0073 0.0123 ± 0.0073
K31             0.0117 ± 0.0070 0.0117 ± 0.0070 0.0118 ± 0.0070
C0 1.4028 ± 0.0827 1.4027 ± 0.0827 1.4027 ± 0.0827 1.8408 ± 0.0412 1.8402 ± 0.0412 1.8402 ± 0.0412 1.9271 ± 0.0754 1.9307 ± 0.0778 1.9311 ± 0.0769
Diagnostics                  
R2 0.9135 0.9135 0.9135 0.9974 0.9974 0.9974 0.9985 0.9985 0.9985
SS 0.2598 0.2598 0.2598 0.0065 0.0065 0.0065 0.0037 0.0037 0.0037
SE 0.1471 0.1471 0.1471 0.0255 0.0255 0.0255 0.0214 0.0214 0.0214
AIC -14.87 -14.87 -14.87 -62.53 -62.53 -62.53 -66.47 -66.47 -66.47
SC -13.59 -13.59 -13.59 -59.98 -59.98 -59.98 -62.64 -62.64 -62.64
*Initial values were arbitrary assigned: K10 = K12 = K21 = K13 = K31 = 0.01; C0=1. Weighting scheme (W=1) was used in all cases. # step size of 5 (mins) was used for numerical integration.  
Table 1: Detailed comparison of XlSimEst results with those of WinNonlin 3.3 and ADAPT II.