過去許多貪汙與民主關係的研究中，大多的問題是忽略或未能解決民主可能存在的內生問題。理論上民主對貪污的影響有正有負，且貪污同樣也會反過來對民主產生影響，而這樣的內生問題在追蹤資料中會對估計結果產生偏誤與不一致。本篇研究採用2001年到2021年共21年，且涵蓋全球198個國家的資料，使用逐步解決內生問題的模式，首先OLS迴歸提供一個存在內生問題的結果；再來使用固定效果模型，克服了未觀察到的變異以及捕捉到個體國家和時間的固定效果；最後是動態追蹤資料系統GMM模型，能更完整解決內生問題及時間動態問題。此外，有別於過去研究在解決內生問題時通常需要從外部尋找工具變數，而尋找有效的工具變數又非一朝一夕之功，系統GMM能從模型內部提取工具變數，省去從外部找尋工具變數的工作。最後得到的結論是民主能抑制貪汙，且兩者為正U型關係。

In the past studies on the relationship between corruption and democracy, most of the problems were that they ignored or failed to solve the possible endogenous problems of democracy. Theoretically, the impact of democracy on corruption is positive or negative, and corruption will also have an impact on democracy in turn, and such endogenous problems will cause bias and inconsistency in the estimation results in the panel data. This study uses data of 21 years from 2001 to 2021 and covers 198 countries around the world. It uses a model to gradually solve endogenous problems. First, OLS regression provides a result with endogenous problems. Second, use a fixed effect model to overcome the unobserved heterogeneity and capture the fixed effects of individual countries and time. Finally, the system GMM model of the dynamic panel data can solve the endogenous problems and time dynamic problems more completely. In addition, unlike previous studies that usually need to find instrumental variables from the outside when solving endogenous problems, furthermore, finding effective instrumental variables is not easy, the system GMM can extract instrumental variables from the inside of the model, eliminating the need to find instrumental variables from the outside. Finally, the conclusion is that democracy can restrain corruption, and the relationship between the two is positive U-shaped.

網頁資料：

1. Transparency International. (2021). Corruption perception index 2020 [Licensed under CCBY-ND 4.0].
http://www.transparency.org/cpi
2. World Bank. (2023). World development indicators.
https://databank.worldbank.org/source/world-development-indicators

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