租稅負擔與地下經濟的門檻效果──台灣的實證研究

Threshold Effects in the Relationship Between the Tax Burden and the Shadow Economy: Evidence from Taiwan

地下經濟與租稅負擔之間存在著緊密的關係。相對於過去文獻大多從線性模型來探討租稅負擔率（或稅率）與地下經濟規模的關係，本文運用非線性的門檻模型（threshold model），以租稅負擔率作為門檻變數，探討租稅負擔率與我國地下經濟規模是否存在非線性關係。實證結果支持台灣的租稅負擔與地下經濟之間存在一個門檻效果，當租稅負擔率低於19.657％時，租稅負擔率的提高將顯著降低地下經濟的規模；但若租稅負擔率高於19.657％，租稅負擔率的上升將顯著提高地下經濟的規模。從樣本內預測能力的評比中，我們也發現門檻模型確實優於線性模型，且門檻模型的結論不因地下經濟的估計方法不同而有所差異。

A close relationship between the tax burden and the shadow economy (SE) has been established in the literature. While most existing studies examine this relationship using a linear model, this paper adopts a non-linear threshold model to identify whether there exists any tax-burden threshold effect for this relationship in Taiwan. We find that there is a threshold effect for the rate of tax burden in this relationship, which is equal to 19.657%. If the rate of tax burden is less than 19.657%, then an increase in the rate of tax burden significantly decreases SE. By contrast, if the rate of tax burden is greater than 19.657%, then a further increase in this rate leads to an increase in SE. In addition, we present results showing that the threshold model outperforms the linear model in terms of in-sample fits, and that the relationship between the tax burden and SE, whether above or below the former's threshold level, is quite robust with respect to different estimation methods for SE.