平台費用改變對行動應用程式多棲性的影響：歐盟數位市場法案之雙重差異法分析

Abstract

《數位市場法》（Digital Markets Act, DMA）由歐盟於2024年施行，旨在透過對被指定為「守門人」（gatekeeper）之數位平台施加相關義務，以促進數位平台生態系之公平性與可競爭性。其中一項重要規範為要求平台降低收費，預期將影響互補者（complementors）的策略行為。本研究探討DMA對行動應用程式經濟中應用開發商之多重歸屬（multihoming）行為及平台差異化之影響。 本研究採用雙重差分法（difference-in-differences, DiD），並使用涵蓋四個歐洲市場（兩個實驗組、兩個對照組）共3,568個源自iOS平台之高營收應用程式資料，歸納出四項主要發現。首先，DMA使多重歸屬比例平均提升3.3個百分點，且此效果在原本即具有較高多重歸屬傾向的類別中更為顯著。其次，與預期相反，對法規反應最為顯著的是低績效應用，而非中等績效應用。第三，以應用程式收益分配之吉尼係數（Gini coefficient）衡量之平台差異化，在DMA實施後呈現小幅上升。最後，法規效果隨時間逐步增強，顯示互補者的調整過程具有遞延性。 本研究對平台治理與數位競爭相關文獻之貢獻，在於說明法規設計如何影響多邊平台生態系中的策略行為。研究結果強調，在評估促進競爭之政策措施時，應納入績效異質性、類別差異及時間動態等因素。對政策制定者與平台管理者而言，應關注不同績效層級之互補者在法規效益吸收上的遞延與不均現象，以作為未來數位市場政策設計與評估之參考。

The Digital Markets Act (DMA), enacted by the European Union in 2024, aims to promote fairness and contestability within digital platform ecosystems by imposing obligations on designated “gatekeeper” platforms. Among its key provisions, the DMA mandates fee reductions that are expected to influence the strategic behavior of complementors. This study investigates the DMA’s impact on app complementors’ multihoming behavior and platform differentiation in the mobile app economy. Using a difference-in-differences (DiD) framework and a dataset of 3,568 top-grossing iOS-origin apps across four European markets (two treated, two control), we identify four key findings. First, the DMA increased multihoming rates by an average of 3.3 percentage points, particularly within high multihoming-prone categories. Second, contrary to expectations, low-performing apps—not medium performers—were most responsive to the regulation. Third, platform differentiation, measured by the Gini coefficient of app revenue distribution, increased modestly following DMA implementation. Finally, the regulation’s effects intensified over time, suggesting a gradual complementor adjustment process. This study contributes to platform governance and digital competition literature by showing how regulatory design influences strategic behavior within multi-sided ecosystems. The findings highlight the importance of accounting for performance heterogeneity, category segmentation, and temporal dynamics when evaluating pro-competition interventions. Policymakers and platform managers should consider the delayed and uneven uptake of regulatory benefits across complementor performance levels to better design and assess future digital market policies.