Fortney John C, Steffick Diane E, Burgess James F, Maciejewski Matt L, Petersen Laura A
VA HSR&D CeMHOR (152/NLR), Central Arkansas Veterans Healthcare System, 2200 Fort Roots Drive, North Little Rock, AR 72114, USA.
Health Serv Res. 2005 Oct;40(5 Pt 1):1422-42. doi: 10.1111/j.1475-6773.2005.00424.x.
To determine whether strategies designed to increase members' use of primary care services result in decreases (substitution) or increases (complementation) in the use and cost of other types of health services.
Encounter and cost data were extracted from the Department of Veterans Affairs (VA) administrative data sources for the period 1995-1999. This timeframe captures the VA's natural experiment of increasing geographic access to primary care by establishing new satellite primary care clinics, known as Community-Based Outpatient Clinics (CBOCs).
We exploited this natural experiment to estimate the substitutability of primary care for other health services and its impact on cost. Hypotheses were tested using ordinary least squares (OLS) regression, which was potentially subject to endogeneity bias. Endogeneity bias was assessed using a Hausman test. Endogeneity bias was accounted for by using instrumental variables analysis, which capitalized on the establishment of CBOCs to provide an exogenous identifier (change in travel distance to primary care).
Demographic, encounter, and cost data were collected for all veterans using VA health services who resided in the catchment areas of new CBOCs and for a matched group of veterans residing outside CBOC catchment areas.
Change in distance to primary care was a significant and substantial predictor of change in primary care visits. OLS analyses indicated that an increase in primary care service use was associated with increases in the use of all specialty outpatient services and inpatient services, as well as increases in inpatient and outpatient costs. Hausman tests confirmed that OLS results for specialty mental health encounters and mental health admissions were unbiased, but that results for specialty medical encounters, physical health admissions, and outpatient costs were biased. Instrumental variables analyses indicated that an increase in primary care encounters was associated with a decrease in specialty medical encounters and was not associated with an increase in physical health admissions, or outpatient costs.
Results provide evidence that health systems can implement strategies to encourage their members to use more primary care services without driving up physical health costs.
确定旨在增加成员对初级保健服务使用的策略是否会导致其他类型卫生服务的使用和成本减少（替代）或增加（互补）。
从退伍军人事务部（VA）1995 - 1999年期间的行政数据源中提取就诊和成本数据。这个时间框架涵盖了VA通过建立新的卫星初级保健诊所（称为社区门诊诊所，CBOCs）来增加初级保健地理可及性的自然实验。
我们利用这个自然实验来估计初级保健对其他卫生服务的可替代性及其对成本的影响。使用普通最小二乘法（OLS）回归检验假设，这可能会受到内生性偏差的影响。使用豪斯曼检验评估内生性偏差。通过使用工具变量分析来解决内生性偏差，该分析利用CBOCs的建立提供一个外生标识符（到初级保健的旅行距离变化）。
收集了所有使用VA卫生服务且居住在新CBOCs服务区域内的退伍军人以及居住在CBOCs服务区域外的一组匹配退伍军人的人口统计学、就诊和成本数据。
到初级保健的距离变化是初级保健就诊变化的一个显著且重要的预测因素。OLS分析表明，初级保健服务使用的增加与所有专科门诊服务和住院服务的使用增加以及住院和门诊成本的增加相关。豪斯曼检验证实，专科心理健康就诊和心理健康住院的OLS结果无偏差，但专科医疗就诊、身体健康住院和门诊成本的结果有偏差。工具变量分析表明，初级保健就诊的增加与专科医疗就诊的减少相关，与身体健康住院或门诊成本的增加无关。
结果提供了证据，表明卫生系统可以实施策略来鼓励其成员使用更多的初级保健服务，而不会推高身体健康成本。
