Blog Archives

Calculate Leave-One-Out Prediction for GLM

December 13, 2015
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Calculate Leave-One-Out Prediction for GLM

In the model development, the “leave-one-out” prediction is a way of cross-validation, calculated as below: 1. First of all, after a model is developed, each observation used in the model development is removed in turn and then the model is refitted with the remaining observations 2. The out-of-sample prediction for the refitted model is calculated

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Fitting Generalized Regression Neural Network with Python

December 9, 2015
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Fitting Generalized Regression Neural Network with Python

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Modeling Frequency in Operational Losses with Python

December 8, 2015
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Modeling Frequency in Operational Losses with Python

Poisson and Negative Binomial regressions are two popular approaches to model frequency measures in the operational loss and can be implemented in Python with the statsmodels package as below: Although Quasi-Poisson regressions is not currently supported by the statsmodels package, we are still able to estimate the model with the rpy2 package by using R

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Modeling Severity in Operational Losses with Python

December 6, 2015
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Modeling Severity in Operational Losses with Python

When modeling severity measurements in the operational loss with Generalized Linear Models, we might have a couple choices based on different distributional assumptions, including Gamma, Inverse Gaussian, and Lognormal. However, based on my observations from the empirical work, the differences in parameter estimates among these three popular candidates are rather immaterial from the practical standpoint.

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Estimating Quasi-Poisson Regression with GLIMMIX in SAS

October 14, 2015
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Estimating Quasi-Poisson Regression with GLIMMIX in SAS

When modeling the frequency measure in the operational risk with regressions, most modelers often prefer Poisson or Negative Binomial regressions as best practices in the industry. However, as an alternative approach, Quasi-Poisson regression provides a more flexible model estimation routine with at least two benefits. First of all, Quasi-Poisson regression is able to address both

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Some Considerations of Modeling Severity in Operational Losses

August 16, 2015
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Some Considerations of Modeling Severity in Operational Losses

In the Loss Distributional Approach (LDA) for Operational Risk models, multiple distributions, including Log Normal, Gamma, Burr, Pareto, and so on, can be considered candidates for the distribution of severity measures. However, the challenge remains in the stress testing exercise, e.g. CCAR, to relate operational losses to macro-economic scenarios denoted by a set of macro-economic

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Are These Losses from The Same Distribution?

June 14, 2015
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Are These Losses from The Same Distribution?

In Advanced Measurement Approaches (AMA) for Operational Risk models, the bank needs to segment operational losses into homogeneous segments known as “Unit of Measures (UoM)”, which are often defined by the combination of lines of business (LOB) and Basel II event types. However, how do we support whether the losses in one UoM are statistically

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Granger Causality Test

May 25, 2015
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Granger Causality Test

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Read A Block of Spreadsheet with R

May 10, 2015
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Read A Block of Spreadsheet with R

In R, there are two ways to read a block of the spreadsheet, e.g. xlsx file, as the one shown below. The xlsx package provides the most intuitive interface with readColumns() function by explicitly defining the starting and the ending columns and rows. However, if we can define a named range for the block in

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To Difference or Not To Difference?

May 9, 2015
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To Difference or Not To Difference?

In the textbook of time series analysis, we’ve been taught to difference the time series in order to have a stationary series, which can be justified by various plots and statistical tests. In the real-world time series analysis, things are not always as clear as shown in the textbook. For instance, although the ACF plot

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