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arXiv 1809.09889q-fin.RMq-fin.ST
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违约概率估计中模型风险和评级动量的捕获与信用评级迁移

Capturing Model Risk and Rating Momentum in the Estimation of Probabilities of Default and Credit Rating Migrations

Marius Pfeuffer, Goncalo dos Reis, Greig smith

摘要:

我们提出了两种方法估计的评级转移概率在马尔可夫和非马尔可夫框架。我们首先估计一个连续时间马尔可夫链使用离散(缺失)的数据,并推导出一个更简单的表达的Fisher信息矩阵,减少计算时间所需的Wald置信区间的一半的因素。我们提供了一个有效的程序,将这种不确定性从马尔可夫链的生成矩阵转移到相应的评级迁移概率,至关重要的是,违约概率。对于我们的第二个贡献,我们假设访问完整的(连续的)数据集,并提出了一个易于处理的和简约的自激标记点过程模型,能够捕捉非马尔可夫效应的评级动量。与马尔可夫模型相比,非马尔可夫模型在投资等级中产生更高的违约概率,但在某些投机等级中也产生更低的违约概率。这两项研究结果与经验观察一致,并具有明确的实际意义。我们说明所有的方法使用穆迪的专有企业信用评级数据集的数据。实现在R包ctmcd中可用。

英文摘要:

We present two methodologies on the estimation of rating transition probabilities within Markov and non-Markov frameworks. We first estimate a continuous-time Markov chain using discrete (missing) data and derive a simpler expression for the Fisher information matrix, reducing the computational time needed for the Wald confidence interval by a factor of a half. We provide an efficient procedure for transferring such uncertainties from the generator matrix of the Markov chain to the corresponding rating migration probabilities and, crucially, default probabilities. For our second contribution, we assume access to the full (continuous) data set and propose a tractable and parsimonious self-exciting marked point processes model able to capture the non-Markovian effect of rating momentum. Compared to the Markov model, the non-Markov model yields higher probabilities of default in the investment grades, but also lower default probabilities in some speculative grades. Both findings agree with empirical observations and have clear practical implications. We illustrate all methods using data from Moody's proprietary corporate credit ratings data set. Implementations are available in the R package ctmcd.

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