所得稅制與勞動供給: 勞動所得抵稅額的模擬研究

Abstract

美國自1975年代小範圍地實施勞動所得租稅抵減制度(Earned Income Tax Credit,EITC),歷經多次立法擴大於各州實施後,目前已經成為美國金額最龐大、成長最快速的重要社會福利制度之一;且因成效良好,EITC也陸續在多國實施。EITC的運作方式係依據勞工的勞動所得金額給予不同的邊際薪資補貼,目地在於激勵無業者投入工作與補貼貧窮的勞動者。 國內結合租稅與勞動供給之研究較稀少,且尚缺乏對於EITC之嚴謹模擬研究,原因可能在於依照勞動所得大小對邊際薪資率補貼或課稅後,勞動者面臨一具折點的分段線性預算限制式(piecewise-linear budget),此時邊際薪資大小與勞動工時有關,如此形狀的預算限制式將造成估計勞動供給函數過程需負擔沉重的計算所致。然而逕以傳統假設預算線形狀為直線形狀的Tobit、OLS法來估計縮減式(reduced form)勞動供給函數將會產生嚴重的內生性問題,該估計結果令人存疑。 本論文第一部分主要參考Triest(1990)的實證方式,採用一般認為能有效解決內生性問題的雙元誤差模型(Two Error Model,TEM),考慮綜合所得稅且以男性優先工作的設定下,首先以一般線性迴歸式估計九十五年家庭收支調查中夫妻之非勞動所得,再用該迴歸式設算九十五年人力運用資料中缺乏的非勞動所得,而後使用TEM估計20-60歲之間已婚夫婦的個別結構式(structured form)勞動供給函數。第二部分設計不同的EITC,加入當年度綜合所得稅的考量下,靜態模擬在這些EITC下對於勞動供給的影響。 本研究發現逕以縮減式估計勞動供給函數如 OLS、Tobit法,將產生嚴重內生性問題,甚至使得參數正負反轉;第二,使用名目工資的OLS或Tobit與TEM法估計結果有明顯不同,且使用TEM法估計下的重要解釋變數之顯著程度將獲得明顯改善,代表勞工確實能夠體認因邊際稅率而改變後的預算線形狀;第三,妻子選擇工時聚集於折點處情況較丈夫明顯,且妻子的替代彈性較丈夫大的多;第四,模擬EITC發現隨著最高抵減額的增加,勞動工時選擇越有向該區段聚集的現象,且區段選擇跳動情況明顯;以最高抵減額48,000元,且遞增遞減率各為40%、20%下,將使得丈夫平均減少6.9%妻子8.4%的勞動供給時數;第五,不論最高抵減額大小,平均而言將使得無業家庭中的60%進入就業市場工作。

Since 1975, Earned Income Tax Credit (EITC) has been executed in some states of America, going through series of expanding act to exercise in many states, nowadays EITC has been one of the largest amount of expending and the most highly growing social welfare program of America. As result of the success of EITC in America, this program has been exercised in many countries successively. The operation of EITC is, depending on the worker’s labor income, giving worker some different rates of subsidy, and the primary purposes of this EITC program are to encourage non-working labor to work and subsidy poor working workers. In Taiwan, the research of combination taxation and labor supply is poor, and such referring research lacks the simulation of EITC. when giving the particular rate of subsidy (like the EITC) or tax (like the comprehensive income tax), the labor will face the kink-point-piecewise-linear budget, and the marginal wage rate depends on the labor hours; this shape of budget constraints will cause the difficulties in the process of estimating labor supply function, and this difficulties may be the reason why this relating research in Taiwan is poor. However, if we directly use traditional econometric method such as Tobit and OLS, which simplify the piece-wise linear to be the linear budget, to estimate the reduced form labor supply will cause serious endogeneity problem and we doubt the estimated results by this traditional way. In the first part of this thesis, mainly referring to the Triest (1990) empirical method, we use the Two Error Model (TEM), which is generally thought can effectively solve the endogeneity problem. First, we use the 95 year Survey of Family Income and Expenditure Data, by OLS method, to estimate the unearned labor income in the 95 year Manpower Survey Statistics data which lacks this unearned labor income. After that, we can use TEM to estimate the 20-60 aged husband and wife structural form labor supply function respectively. In the second part, we design different EITC programs, considering the comprehensive income tax, then statically simulate the effect of this EITC programs. This research finds that directly using the Tobit and OLS method to estimate will cause serious endogeneity problems, even causing the sign of estimated parameters been changed. Second, we find that the estimated results are obviously different between the OLS or Tobit which estimate using the nominal wage rate and the TEM, and the TEM could improve the statistical significance of those important economic independent variable, it seems that the worker could understand themselves entire piecewise-linear budget constraints. Third, wife chooses labor hours are more gathering at kink point than husband does, and wife’s elasticity of substitution is bigger than husband’s. Fourth, by the simulation of the EITC, we find that when the biggest tax credit rising, workers choose their labor hours will be more gathering the biggest tax credit region, and their changes of choosing piece-wise budget regions are very obviously. When the biggest tax credit is 48,000, phase-in and phase-out rate are 40% and 20% respectively, this EITC program could cause husband and wife on average reduce 6.9% and 8.4% labor hours respectively. Finally, no matter what the biggest tax credit is, on average, the EITC program will encourage about 60% non-working family to work.