Table 1.

Description of Data by Physician Organization

	Physician Organization 1	Physician Organization 2	Physician Organization 3	Physician Organization 4
Location	California	New York	Ohio	Idaho
HMO penetration in market area	50.1%	23.3%	21.0%	13.1%
Method of PCP reimbursement	Partial Capitation	Fee-For-Service	Fee-For-Service	Partial Capitation
PCP services capitated by HMOs in market area:
Solo/Single Spec. Group	66.4%	35.0%	46.4%	85.7%
Multi-Spec. Group	85.4%	47.8%	60.9%	95.2%
Dates covered by data	Jan.–Dec. 1994	Jan.–Dec. 1995	Apr. 1994 Mar. –1995	Jan.–Dec. 1995
Number of PCPs	662	341	180	208
Number of enrollees age 21–64	51,811	39,166	50,845	12,907
Number of enrollees continuously enrolled for six months (%)	35,235(68.0%)	20,076(51.3%)	33,031(65.0%)	7,065(54.7%)
Percent of continuously enrolled enrollees with at least 1 service in claims data	91.3%	83.8%	79.8%	96.4%
Number of continuously enrolled enrollees with at least 2 encounters (%)	27,217(77.2%)	14,124(70.4%)	21,213(64.2%)	4,706(66.6%)
Number of continuously enrolled enrollees excluded because only 1 patient seen by PCP	13	9	14	29
Number of continuously enrolled enrollees excluded because claims data shows more than 1 PCP on given date	38	25	1	0
Number of continuously enrolled enrollees (patients) included in analyses	27,166	14,090	21,198	4,677
Number of patients randomized to estimation dataset	13,477	6,779	9,582	2,109
% patients switching PCPs	6.8%	4.9%	0.4%	7.1%
% encounters that are switches from previous encounter	1.6%	1.3%	0.2%	2.1%