本文引用Hansen (1999) 門檻模型，針對1960 年至2005 年62個國家資料作橫斷面分析，客觀估計貿易自由化對高、低所得國家之所得分配影響。實證結果指出在低所得國家商品自由化致會惡化國內所得分配，在高所得國家商品自由化大致上對國內所得分配無顯著影響；而外人直接投資對低所得國家所得分配無影響，在高所得國家外人直接投資將顯著惡化國內所得分配。此結果意味著各國可依其經濟發展程度適當地調整開放政策，以利國內長期經濟發展與所得分配。

This paper empirically investigates the threshold effects of openness on income inequality. Specifically, we use Hansen’s (1999)threshold regression model to examine whether the openness-inequality link varies with the degree of a country’s income. By applying the model to 62 countries during the period 1996-2005, we find that there indeed exists an income threshold in the openness-inequality link.Moreover, the opening of goods markets increases income inequality in low-income countries. However, in high-income ones trade openness has minor effects. By contrast, foreign direct investment is found to increase income inequality in high-income countries and has an unimportant effect in low-income ones. These findings suggest that to reduce income inequality, the governments need to consider their positions in the economic development process and adopt relevant openness strategies.