論文摘要：
研究背景：隨著台灣醫療市場集團化趨勢日益明顯，醫院屬於集團醫院是否有助於提升病患醫療結果成為值得探討的議題。
研究目的：本研究旨在探討台灣醫療市場中，醫院是否屬於集團體系對急性心肌梗塞（Acute Myocardial Infarction, AMI）病患接受到醫療品質之影響，並進一步分析市場競爭程度在其中所扮演之調節角色。
研究方法：本研究的設計為重複橫斷性研究設計（repeated cross-sectional study design），採用1998年至2020年全民健康保險資料庫之全國性資料，觀察病患住院後七日、十四日、三十日內死亡情形與出院後三十日、六十日、九十日內再住院情形作為品質衡量指標；醫院集團的定義為研究者自行整理，集團醫院體系大致上分為法人型集團、醫學中心領導型集團、署立醫院體系。結合醫院是否為集團成員。調節變項為醫院所在地的市場競爭程度，以行政疆界法搭配賀芬達指標（Herfindahl-Hirschman Index, HHI）。採用廣義線性模型（與後面的分析模型一致），並控制病患特性（年齡、性別、社會經濟地位、合併症指標）、醫院特性（醫院權屬別、醫院所在地區）與地區特性（地區平均每人平均可支配所得），控制時間固定效果以及醫院群組變異數與共變異數矩陣。
研究結果：本研究的實證結果顯示，在台灣的醫療市場環境下，集團醫院相較於非集團醫院而言有較低之死亡風險（七日內odd ratios [OR]值0.824；95% confidence interval [CI]：0.799-1.850、十四日內OR值0.862；95%CI：0.839-0.855、三十日內OR值0.908；95%CI：0.879-0.956）與再住院風險（三十日OR值：0.867；95% CI：0.848-0.887、六十日OR值0.849；95% CI：0.833-0.866、九十日OR值0.886；95% CI：0.869-0.902）。在市場集中度較高的地區也有較低之死亡風險（七日內OR值0.949；95%CI：0.912-0.987、十四日內OR值0.955；95% CI：0.923-0.988）與再住院風險（六十日OR值0.971；95% CI：0.947-0.996、九十日OR值0.955；95% CI：0.945-0.991）。此外在三十日死亡風險中市場競爭程度對集團醫院之品質影響具有修飾效果（OR = 1.067；95% CI：1.018–1.118），當市場越集中時，集團醫院與醫療品質之間的關係被減緩了。
研究結論與建議：集團醫院在台灣醫療體系中具有相當影響力，其整合帶來的資源共享與規模經濟，確實有助於提升整體醫療品質。然而，市場競爭結構對於此一品質效果的調節作用僅在三十日死亡風險情形呈現明顯效果，其結果並非在所有品質指標間一致。此一現象顯示，集團化與市場競爭之間的互動關係，可能尚受到其他制度設計、醫院內部管理模式或病患組成等多重因素的影響，未來仍有進一步探討與驗證的空間。由於本研究採用重複橫斷性研究設計，無法精確的觀察某間醫院加入集團體系前後的差別，因此建議在可挑出幾間加入集團體系的醫院進行相關研究。

Background: With the increasing trend of hospital consolidation in Taiwan’s healthcare market, whether affiliation with a multihospital system enhances patient outcomes has become a critical issue for investigation.
Objective: This study aims to examine the impact of hospital affiliation with a multihospital system on the quality of care received by patients with acute myocardial infarction (AMI) in Taiwan and to further assess the moderating effect of market competition.
Methods: Adopting a repeated cross-sectional study design, this research uses nationwide data from Taiwan’s National Health Insurance Research Database spanning 1998 to 2020. Healthcare quality is measured by patient mortality within 7, 14, and 30 days of admission, and readmission within 30, 60, and 90 days after discharge. Hospitals affiliated with multihospital was compiled by the author and categorized into nonprofit hospital systems, academic medical center–led systems, and government-owned hospital networks. Market competition was measured using the Herfindahl-Hirschman Index (HHI) based on administrative boundaries. Generalized estimating equations were employed, controlling for patient characteristics (age, sex, socioeconomic status, comorbidity index), hospital characteristics (ownership type, location), regional characteristics (average disposable income), time fixed effects, and clustering by hospital group variance-covariance structures.
Results: Empirical findings show that hospitals affiliated with a multihospital system are associated with lower risks of mortality (7-day OR = 0.824; 95% CI: 0.799–0.850; 14-day OR = 0.862; 95% CI: 0.839–0.885; 30-day OR = 0.908; 95% CI: 0.879–0.956) and readmission (30-day OR = 0.867; 95% CI: 0.848–0.887; 60-day OR = 0.849; 95% CI: 0.833–0.866; 90-day OR = 0.886; 95% CI: 0.869–0.902), compared to non-affiliated hospitals. In highly concentrated markets, mortality (7-day OR = 0.949; 95% CI: 0.912–0.987; 14-day OR = 0.955; 95% CI: 0.923–0.988) and readmission risks (60-day OR = 0.971; 95% CI: 0.947–0.996; 90-day OR = 0.955; 95% CI: 0.945–0.991) were also lower. Additionally, a significant interaction effect between market competition and hospital affiliation was found for 30-day mortality (OR = 1.067; 95% CI: 1.018–1.118), indicating that the quality advantage of multihospital system affiliation was reduced in more concentrated markets.
Conclusion: Hospitals affiliated with multihospital systems play a vital role in Taiwan’s healthcare sector. Their integrated operations and scale economies indeed contribute to higher care quality. However, the moderating effect of market competition is not consistent, particularly in readmission-related indicators, where no stable pattern was observed. These findings suggest that the interaction between Hospitals affiliated with multihospital and competition may be influenced by institutional settings, hospital management models or patient case-mix. Further research is needed to clarify these mechanisms. Given the use of a repeated cross-sectional design, this study cannot track the before-and-after effects of hospitals joining a system. Future studies are recommended to focus on hospitals with observable system-entry events.

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