人口變遷與台灣家戶收入不平等

Abstract

台灣家戶收入在過去30年間變得越來越不平等，多數經濟學解釋將之歸因於勞動市場的變化，本研究則強調人口變遷的影響。我使用1981至2006年主計處家庭收支調查資料，並採取以分量迴歸（Quantile Regression）為基礎的反事實分析方法（Bishop et al. 1997；Machado and Mata 2005）探究年齡、教育、婚姻狀況、家戶規模等人口因素對家戶收入不平等的效果。我首先分析1981至2000年間家戶收入不平等的變化模式，其次探討各種人口因素對歷年家戶總收入吉尼係數的邊際效果及其跨時變化，最後將家戶收入不平等趨勢分解為人口組成變化效果與報酬結構變化效果，比較兩者的相對貢獻。結果發現：台灣家戶收入差異擴大的主要來源是經濟弱勢家戶收入成長率顯著低於全國家戶收入的平均成長率；而戶長年齡、戶內就業人數以及戶長為大學畢業等因素對於不平等有較大的影響，且影響力有逐年增加的趨勢，其中又以戶長年齡效果增加的幅度最大。整體而言，我國家戶收入不平等的成長主要來自於人口組成的改變，報酬結構變化雖然也會增加不平等，但效果相對很小。報酬結構的變化大幅提昇了所有階層的家戶收入，但人口組成的改變格外不利於經濟弱勢家戶，導致整體收入不平等持續惡化。

Taiwan experienced significant increases in the degree of income inequality over the past three decades. This trend has renewed interest in the study of the factors that may explain changes in income inequality. In this thesis, I focus on the effects of demographic change. I use the Survey of Family Income and Expenditure (SFIE) data for the period 1981-2006. I apply counterfactual decomposition methods (Bishop et al. 1997；Machado and Mata 2005) based on conditional quantile regressions to investigate the effects of demographic factors on income inequality. The results show that the impact of age was quite substantial. The effects of age, college education, marital status, and number of earners in the household on income inequality have grown lager across time, while the influence of household size has decline. I further decompose the trend of income inequality into changes in the composition of demographic characteristics and changes in the return to these characteristics. I find evidence that changes in the demographic composition in 1980s and 1990s are responsible for the rising inequality. In contrast, changes in the return have only a minor role. Thus the main driving force of rising inequality is the change in demographic composition.