本文使用 1991年到 2015年美國上市公司的資料檢測顧客集中度風險與財務槓桿調整速度的關係。提出假說企業型主要顧客會使供應商面對較高的潛在風險，進而透過增加財務槓桿調整速度，以面對往後可能面對的問題；政府型主要顧客則因為對供應商有較多正面的影響，所以供應商 可能增加調整速度的幅度沒有企業型的大，甚至不需要增
加槓桿調整速度。實證證據表示，企業型主要顧客確實會增加槓桿的調整速度，政府型主要顧客則也會增加槓桿調整速度， 而前者所增加的速度確實比後者要來的快一些， 主要解釋變數的結果在所有模型上都有經濟和統計上的顯著性。

本研究使用虛擬變數、銷售比率與 HHI指標三種方式來測量顧客集中度，使用縮減式部分調整模型來評估槓桿調整速度，並使用 DPF預估法來解決負債比率的不偏性。作為延伸檢驗，發現高顧客集中度造成的影響會大於低顧客集中度，高轉換成本下企業型顧客集中度的效果會消失，收入多角化能使企業型顧客集中度對槓桿調整速度的效果減
少，政府支出的高成長也會減少政府型顧客集中度對調整速度的影響。

This paper selects data from American listed companies from 1991 to 2015 to test the relationship between the customer concentration risk and the leverage speed of adjustment. It is hypothesized that the main customers of the enterprise will make the higher potential risks of the suppliers, and then increase the leverage speed of adjustment to face the problems that may happen in the future. The main customers of the government have more positive impact on the suppliers, so the supplier increase the leverage speed of adjustment smaller than the customer of enterprise. The empirical evidence shows that the main customers of the enterprise will increase the leverage speed of adjustment, while the main customers of government will also increase the leverage speed of adjustment. The results of main explanatory variables are economically and statistically significant on all models.

In this study, the dummy variable, sales ratio and HHI index were used to measure customer concentration. The reduced-form partial adjustment model was used to evaluate the leverage speed of adjustment, and the DPF estimation approach method was used to solve the unbiasedness of debt ratio. As an extension test, it is found that the impact of high customer concentration will be greater than the low customer concentration, the effect of enterprise customer concentration will disappear under high switching costs, and the diversification of revenue can reduce the effect of enterprise customer concentration on leverage speed of adjustment. The high growth of government spending will also reduce the impact of government-type customer concentration on adjustment speed.

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