本文以新北市與桃園市由縣逐步進入直轄市改制之歷程作為制度變化，探討歲出、自籌財源、無條件補助款及補助依賴度之變化，並檢驗捕蠅紙效果。研究使用2001年至2023年臺灣縣市追蹤資料，分別以新北市2008年及桃園市2011年開始準用直轄市相關規定之年度作為政策起點。實證上先以差異中之差異法 (difference-in-differences, DID) 進行初步估計；鑑於部分結果變數之政策前平行趨勢未獲充分支持，進一步採用合成控制法 (synthetic control method, SCM) 建構反事實路徑，並以空間安慰劑檢定及均方根預測誤差 (Root Mean Squared Prediction Error, RMSPE) 比值評估估計結果。最後，以歲出gap為依變數，自籌財源gap與無條件補助款gap為解釋變數進行迴歸，並以Wald檢定比較係數差異。
結果顯示，兩市進入直轄市改制歷程後，歲出、自籌財源與無條件補助款多數年度均高於合成控制值，其中歲出與自籌財源之正向差距較為持續，無條件補助款則於政策初期增加後逐漸收斂。捕蠅紙效果檢驗顯示，自籌財源gap與無條件補助款gap均與歲出gap呈顯著正向關係，但自籌財源係數顯著高於無條件補助款係數，因此未支持典型捕蠅紙效果。補充分析亦發現，兩市正式升格後多數年度之補助依賴度低於合成控制值。整體而言，本文結果顯示，新北市與桃園市進入直轄市改制歷程後，地方財政規模與財源結構均有所調整，且歲出與自籌財源之連動程度高於無條件補助款，因此未支持典型捕蠅紙效果；正式升格後，中央移轉財源占歲出之相對比重亦呈下降。

This study examines the upgrading process of New Taipei City and Taoyuan City from counties to special municipalities as an institutional change, focusing on changes in local government expenditure, own-source revenue, unconditional grants, and grant dependency, and investigates whether the flypaper effect is present. Using county- and city-level panel data in Taiwan from 2001 to 2023, the study defines 2008 for New Taipei City and 2011 for Taoyuan City, when the two jurisdictions began applying relevant regulations governing special municipalities, as their respective policy intervention years. Difference-in-differences (DID) estimation is first employed as a preliminary analysis. Because the parallel trends assumption is not sufficiently supported for some outcome variables, the synthetic control method (SCM) is subsequently used to construct counterfactual trajectories. The results are further assessed using in-space placebo tests and post- to pre-treatment root mean squared prediction error (RMSPE) ratios. Finally, the expenditure gap is regressed on the own-source revenue gap and the unconditional grant gap, and a Wald test is used to examine whether the two coefficients differ significantly.
The results show that, after the two jurisdictions entered the municipal upgrading process, expenditure, own-source revenue, and unconditional grants were above their corresponding synthetic control values in most years. The positive gaps in expenditure and own-source revenue were relatively persistent, whereas the gap in unconditional grants increased during the early post-treatment period and gradually converged thereafter. The flypaper-effect analysis shows that both the own-source revenue gap and the unconditional grant gap are positively and significantly associated with the expenditure gap. However, the coefficient on the own-source revenue gap is significantly larger than that on the unconditional grant gap, providing no support for the conventional flypaper effect. Supplementary analysis also shows that, after the two jurisdictions were formally upgraded to special municipalities, their grant dependency ratios were below the corresponding synthetic control values in most years. Overall, the results indicate that the municipal upgrading process of New Taipei City and Taoyuan City was accompanied by changes in both the scale and composition of local public finances. Expenditure was more strongly associated with own-source revenue than with unconditional grants, and thus the results do not support the conventional flypaper effect. Following formal upgrading, the relative share of central government transfers in local expenditure also declined.

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