Blog Archives

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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Modeling Count Time Series with tscount Package

March 31, 2015
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Modeling Count Time Series with tscount Package

The example below shows how to estimate a simple univariate Poisson time series model with the tscount package. While the model estimation is straightforward and yeilds very similar parameter estimates to the ones generated with the acp package (https://statcompute.wordpress.com/2015/03/29/autoregressive-conditional-poisson-model-i), the prediction mechanism is a bit tricky. 1) For the in-sample and the 1-step-ahead predictions: yhat_

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rPithon vs. rPython

March 30, 2015
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rPithon vs. rPython

Similar to rPython, the rPithon package (http://rpithon.r-forge.r-project.org) allows users to execute Python code from R and exchange the data between Python and R. However, the underlying mechanisms between these two packages are fundamentally different. Wihle rPithon communicates with Python from R through pipes, rPython accomplishes the same task with json. A major advantage of rPithon

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Autoregressive Conditional Poisson Model – I

March 29, 2015
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Autoregressive Conditional Poisson Model – I

Modeling the time series of count outcome is of interest in the operational risk while forecasting the frequency of losses. Below is an example showing how to estimate a simple ACP(1, 1) model, e.g. Autoregressive Conditional Poisson, without covariates with ACP package.

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Ensemble Learning with Cubist Model

March 20, 2015
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Ensemble Learning with Cubist Model

The tree-based Cubist model can be easily used to develop an ensemble classifier with a scheme called “committees”. The concept of “committees” is similar to the one of “boosting” by developing a series of trees sequentially with adjusted weights. However, the final prediction is the simple average of predictions from all “committee” members, an idea

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Model Segmentation with Cubist

March 18, 2015
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Model Segmentation with Cubist

Cubist is a tree-based model with a OLS regression attached to each terminal node and is somewhat similar to mob() function in the Party package (https://statcompute.wordpress.com/2014/10/26/model-segmentation-with-recursive-partitioning). Below is a demonstrate of cubist() model with the classic Boston housing data.

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