Credit scorecard using Logistic Regression on R

Question

I tried developing a scorecard to assess creditworthiness using the "Scorecard" package on R. The problem I encountered is when I scale the card and calculate the points for each attribute of each characteristic: when I calculate the score through the package I get one score, but when I do the scaling myself and calculate the score manually I get another score. I'm not sure if the package uses a different methodology or if I did something wrong.

Here's the code of the calculation done through the package:

library(scorecard)

# load germancredit data
data("germancredit")
summary(germancredit)

# filter attributes:
filtered_data = var_filter(germancredit, y="creditability")

# breaking data into train and test by creating two sub-objects "Train" and "Test" using the  split function
dt_list = split_df(filtered_data, y="creditability", ratio = 0.6, seed = 30)

#Storing the two sub-objects created by last function in separate variables
train = dt_list$train
test = dt_list$test

# Automatic Optimal WoE binning
binned_data = woebin(filtered_data, y="creditability")

#adjusting breaks
breaks_adj = list(
  age.in.years=c(26, 35, 40),
  other.debtors.or.guarantors=c("none", "co-applicant%,%guarantor"))

bins_adj = woebin(filtered_data, y="creditability", breaks_list=breaks_adj)


# Converting train and test into WoE values: all values of each attributes
# are replaced by their respective WoE values already calculated
train_woe = woebin_ply(train, bins_adj)
test_woe = woebin_ply(test, bins_adj)

# Logistic Regression applied to the training data that we converted to WoE values:
m1 = glm( creditability ~ ., family = binomial(), data = train_woe)

# Show estimated coefficients and significance level of each attribute:
summary(m1)


# Scorecard Scaling & final card:
card = scorecard(bins = binned_data, m1, points0 = 600, odds0 = 50, pdo = 20)

But when I calculate the score manually for example for the attribute "Rent" of the "Housing" characteristic as such (following Siddiqi (2006), Credit Risk Scorecards):

#for rent attribute:
Housing_coeff = 0.120110
rent_woe = 0.4044452
intercept = -0.9419
num_of_charac = 14
pdo = 20
factor = pdo/log(2)
offset = 600 - (factor*log(50))

#Score rent
(Housing_coeff*rent_woe + (intercept/num_of_charac) ) * factor + (offset/num_of_charac)

I have a way different score than the one given by the package. Also some of the scores given by the package are negative and I don't know if that's supposed to be.

Thanks.

Answer 1

Nevermind I found the answer. I looked into the source code and the package uses a slightly different methodology than the "standard" one.