Table 2. Comparison of Payment Estimates for Laparoscopic vs Open Colectomy Using Conventional Multivariable and Instrumental Variable Models.

Variable	US $			P Value
	Laparoscopic Surgery	Open Surgery	Average (95% CI) Treatment Effect
Total Episode Payments
Multiple linear regression	17 161	26 062	−5547 (−5408 to −5684)	<.01
Instrumental variable analysis	20 452	24 573	−3676 (−2444 to −4907)	<.01
Index Hospitalization Payments
Multiple linear regression	13 016	18 502	−3419 (−3724 to −3151)	<.01
Instrumental variable analysis	15 077	17 570	−335 (−842 to 254)	.38
Physician Payments
Multiple linear regression	2019	2798	−402 (−356 to −461)	<.01
Instrumental variable analysis	2249	2694	−292 (−180 to 304)	<.01
Readmission Payments
Multiple linear regression	9284	10 429	−840 (−623 to −1016)	<.01
Instrumental variable analysis	9791	10 292	−5642 (−3245 to −7986)	<.01
Postacute Care Payments
Multiple linear regression	1204	3029	−1109 (−824 to −1457)	<.01
Instrumental variable analysis	1850	2737	−1446 (−1988 to −935)	<.01