在亞洲國家或者一些高存款率的國家中，部分提前清償（partial prepayment，又稱curtailment）是一個很普遍的現象。當借款者有多餘資金時，通常會用以償還貸款本金，以減少利息支付。在台灣的貸款資料亦可發現有顯著的curtailment現象，本研究遂將curtailment納入影響變數加以探討。事實上，貸款年齡對提前清償率及違約率的影響型態不同，隨貸款年齡增加，提前清償率成S型曲線增加，而違約率則先遞增再遞減，類似Gamma分配。針對此特性，本研究以separate logit模型分別探討各解釋變數對條件提前清償率及條件違約率之影響，同時影響提前清償及違約之變數隨時間動態調整，更精確捕捉貸款者的還款行為，以精確估計提前清償及違約率。

In Asian Countries or some countries with high saving rates, partial prepayment, curtailment, is a common payment behavior. When borrowers have extra money more than the basic living needs, they usually use that additional amount to repay the principle early in order to curtail the loan balance and also reduce the interest payment. Based on mortgage loan-level data obtained from a commercial bank in Taiwan, we find the curtailment effect is material. Therefore, we incorporate the curtailment factor into the explanatory variables in analysis. More specifically, the aging patterns of prepayment rate and default rate are different. The prepayment rate exhibits a “S” shape; whereas the default rates initially increase progressively and then decrease thereafter similar to a Gamma distribution. By using the separate logit model with age functions accordingly, we can capture the borrowers’ payment behavior, and accurately estimate the prepayment and default rates.

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