- Credit Risk Modelling - Case Studies
- Classification vs. Regression Models
- Case Study - German Credit - Steps to Build a Predictive Model
- Import Credit Data Set in R
- German Credit Data : Data Preprocessing and Feature Selection in R
- Credit Modelling: Training and Test Data Sets
- Build the Predictive Model
- Logistic Regression Model in R
- Measure Model Performance in R Using ROCR Package
- Create a Confusion Matrix in R
- Credit Risk Modelling - Case Study- Lending Club Data
- Explore Loan Data in R - Loan Grade and Interest Rate
- Credit Risk Modelling - Required R Packages
- Loan Data - Training and Test Data Sets
- Data Cleaning in R - Part 1
- Data Cleaning in R - Part 2
- Data Cleaning in R - Part 3
- Data Cleaning in R - Part 5
- Remove Dimensions By Fitting Logistic Regression
- Create a Function and Prepare Test Data in R
- Building Credit Risk Model
- Credit Risk - Logistic Regression Model in R
- Support Vector Machine (SVM) Model in R
- Random Forest Model in R
- Extreme Gradient Boosting in R
- Predictive Modelling: Averaging Results from Multiple Models
- Predictive Modelling: Comparing Model Results
- How Insurance Companies Calculate Risk

## Credit Risk - Logistic Regression Model in R

To build our first model, we will tune Logistic Regression to our training dataset.

First we set the seed (to any number. we have chosen 100) so that we can reproduce our results.

Then we create a downsampled dataset called `samp`

which contains an equal number of `Default`

and `Fully Paid`

loans. We can use the `table()`

function to check that the downsampling is done correctly.

```
> set.seed(100)
> samp = downSample(data_train[-getIndexsOfColumns(data_train, c( "loan_status") )],data_train$loan_status,yname="loan_status")
> table(samp$loan_status)
Default Fully.Paid
12678 12678
>
```

We will now choose a small set of data for tuning the model.

```
#choose small data for tuning
train_index = createDataPartition(samp$loan_status,p = 0.05,list=FALSE,times=1)
```

We will use the functions available in the caret package to train the model.

**Step 1: We setup the control parameter to train with the 3-fold cross validation (cv)**

```
ctrl <- trainControl(method = "cv",
summaryFunction = twoClassSummary,
classProbs = TRUE,
number = 3
)
```

**Step 2: We train the classification model on the data**

```
glmnGrid = expand.grid(.alpha = seq(0, 1, length = 10), .lambda = 0.01)
glmnTuned = train(samp[train_index,-getIndexsOfColumns(samp,"loan_status")],y = samp[train_index,"loan_status"],method = "glmnet",tuneGrid = glmnGrid,metric = "ROC",trControl = ctrl)
```

**Advanced Notes**

We use Elastic Net regularization, which comprises of Ridge and Lasso regularization, with cross-validation to prevent overfitting. Our goal is maximizing AUC. Learn more about Regularization here.

Due to limited computation resource, we run model tuning on small data and fixed lambda parameter. We use small fold: 3-fold cross validation. We then refit the best model with the whole data.

(Note: we put the final tuning result here instead of running through the whole process. We disable the execution of tuning code although readers can enable it back by setting eval = TRUE )

### Look Inside glmTuned

We can now examine the output of the generated model.

```
plot(glmnTuned)
```

```
> glmnTuned
glmnet
1268 samples
70 predictor
2 classes: 'Default', 'Fully.Paid'
No pre-processing
Resampling: Cross-Validated (3 fold)
Summary of sample sizes: 846, 844, 846
Resampling results across tuning parameters:
alpha ROC Sens Spec
0.0000000 0.6754917 0.6261588 0.6261215
0.1111111 0.6753332 0.6245939 0.6261215
0.2222222 0.6755427 0.6293332 0.6340055
0.3333333 0.6753729 0.6277609 0.6371725
0.4444444 0.6763833 0.6277609 0.6356002
0.5555556 0.6772067 0.6277609 0.6387523
0.6666667 0.6774650 0.6230290 0.6387746
0.7777778 0.6777457 0.6214567 0.6372023
0.8888889 0.6780438 0.6230365 0.6372023
1.0000000 0.6782664 0.6277758 0.6356300
Tuning parameter 'lambda' was held constant at a value of 0.01
ROC was used to select the optimal model using the largest value.
The final values used for the model were alpha = 1 and lambda = 0.01.
>
```

The best penalty parameter is alpha = 1 (more weight on Ridge) with fixed shrinking lambda = 0.01. We use this parameter to retrain the whole sample.

```
library(glmnet)
model = glmnet(
x = as.matrix(samp[-getIndexsOfColumns(samp,"loan_status")]),
y=samp$loan_status,
alpha = 1,
lambda = 0.01,
family = "binomial",
standardize = FALSE)
```

The finalized Logistic Regression model is applied to the test loan data. We look at ROC graph and AUC. We also set probability prediction cutoff at 50% (noted that the higher this value is, the more likely the loan is Fully Paid) and collect some performance metrics for a later comparison.

```
table_perf = data.frame(model=character(0),
auc=numeric(0),
accuracy=numeric(0),
sensitivity=numeric(0),
specificity=numeric(0),
kappa=numeric(0),
stringsAsFactors = FALSE
)
```

```
predict_loan_status_logit = predict(model,newx = as.matrix(data_test[-getIndexsOfColumns(data_test,"loan_status")]),type="response")
```

### ROC and AUC

```
library(pROC)
rocCurve_logit = roc(response = data_test$loan_status,
predictor = predict_loan_status_logit)
auc_curve = auc(rocCurve_logit)
```

```
plot(rocCurve_logit,legacy.axes = TRUE,print.auc = TRUE,col="red",main="ROC(Logistic Regression)"
```

```
> rocCurve_logit
Call:
roc.default(response = data_test$loan_status, predictor = predict_loan_status_logit)
Data: predict_loan_status_logit in 5358 controls (data_test$loan_status Default) < 12602 cases (data_test$loan_status Fully.Paid).
Area under the curve: 0.7031
>
```

```
> predict_loan_status_label = ifelse(predict_loan_status_logit<0.5,"Default","Fully.Paid")
> c = confusionMatrix(predict_loan_status_label,data_test$loan_status,positive="Fully.Paid")
> table_perf[1,] = c("logistic regression",
round(auc_curve,3),
as.numeric(round(c$overall["Accuracy"],3)),
as.numeric(round(c$byClass["Sensitivity"],3)),
as.numeric(round(c$byClass["Specificity"],3)),
as.numeric(round(c$overall["Kappa"],3))
)
> rm(samp,train_index)
> tail(table_perf,1)
model auc accuracy sensitivity specificity kappa
1 logistic regression 0.703 0.645 0.643 0.65 0.256
>
```

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