Table 2.

Final Boosted Regression Trees and Main Effects Linear Models

						Mean Cost (Dollars)†
			Percent of Variance Explained†				Predicted
Year	Plan Type	Nodes/Tree*	Boosted Trees	Main Effects	Gain‡	Observed	Boosted Trees	Main Effects
2001	Indemnity	9	49.7	47.2	2.5	4,005	3,986	4,007
	PPO	9	52.1	47.6	4.5	3,141	3,136	3,157
	POS	6	49.8	42.5	7.3	2,787	2,783	2,805
2002	Indemnity	8	17.7	16.6	1.1	4,141	4,184	4,216
	PPO	12	15.2	14.2	1.0	3,898	3,885	3,910
	POS	2	15.2	14.8	0.4	2,953	2,982	2,994

^*Number of terminal nodes per tree in final boosted regression trees model.

^†Based on test samples.

^‡Gain=percent of variance explained by tree boosting minus percent explained by main effects.

POS, point-of-service; PPO, preferred provider organization.