  After a debt has been legally declared "uncollectable" by a bank,
the account is considered "charged-off."
But that doesn't mean the bank walks away from the debt.
They still want to collect some of the money they are owed.
The bank will score the account to assess the expected recovery amount, that is,
the expected amount that the bank may be able to receive from the customer in the future.
This amount is a function of the probability of the customer paying, the total debt,
and other factors that impact the ability and willingness to pay.
  The bank has implemented different recovery strategies at different thresholds ($1000, $2000, etc.) where the greater the expected recovery amount, the more effort the bank puts into contacting the customer. For low recovery amounts (Level 0), the bank just adds the customer's contact information to their automatic dialer and emailing system. For higher recovery strategies, the bank incurs more costs as they leverage human resources in more efforts to obtain payments. Each additional level of recovery strategy requires an additional $50 per customer so that customers in the Recovery Strategy Level 1 cost the company $50 more than those in Level 0. Customers in Level 2 cost $50 more than those in Level 1, etc.
The big question: does the extra amount that is recovered at the higher strategy level exceed the extra $50 in costs? In other words, was there a jump (also called a "discontinuity") of more than $50 in the amount recovered at the higher strategy level?
df = pd.read_csv("datasets/bank_data.csv" )
df.head()| id | expected_recovery_amount | actual_recovery_amount | recovery_strategy | age | sex | |
|---|---|---|---|---|---|---|
| 0 | 2030 | 194 | 263.540 | Level 0 Recovery | 19 | Male |
| 1 | 1150 | 486 | 416.090 | Level 0 Recovery | 25 | Female |
| 2 | 380 | 527 | 429.350 | Level 0 Recovery | 27 | Male |
| 3 | 1838 | 536 | 296.990 | Level 0 Recovery | 25 | Male |
| 4 | 1995 | 541 | 346.385 | Level 0 Recovery | 34 | Male |
Quick summary of the Levels and thresholds again:
- Level 0: Expected recovery amounts >$0 and <=$1000
- Level 1: Expected recovery amounts >$1000 and <=$2000
- The threshold of $1000 separates Level 0 from Level 1
Expected Recovery Amount that also varied systematically across the $1000 threshold.How about
age?
plt.scatter(x=df['expected_recovery_amount'], y=df['age'], c="g", s=2)
plt.xlim(0, 2000)
plt.ylim(0, 60)
plt.show()
  We want to convince ourselves that variables such as age and sex
are similar above and below the $1000 Expected Recovery Amount threshold.
This is important because we want to be able to conclude that differences
in the actual recovery amount are due to the higher Recovery Strategy and
not due to some other difference like age or sex.
from scipy import stats
# average age just below and above the threshold
era_900_1100 = df.loc[(df['expected_recovery_amount']<1100) &
(df['expected_recovery_amount']>=900)]
by_recovery_strategy = era_900_1100.groupby(['recovery_strategy'])
by_recovery_strategy['age'].describe().unstack()
# Kruskal-Wallis test
Level_0_age = era_900_1100.loc[df['recovery_strategy']=="Level 0 Recovery"]['age']
Level_1_age = era_900_1100.loc[df['recovery_strategy']=="Level 1 Recovery"]['age']
>>> print(stats.kruskal(Level_0_age,Level_1_age))
... KruskalResult(statistic=3.4572342749517513, pvalue=0.06297556896097407)Â Â We have seen that there is no major jump in the average customer age just above and just below the $1000 threshold by doing a statistical test as well as exploring it graphically with a scatter plot.
  We want to also test that the percentage of customers that are male does not jump across the $1000 threshold. We can start by exploring the range of $900 to $1100 and later adjust this range.
# Number of customers in each category
crosstab = pd.crosstab(df.loc[(df['expected_recovery_amount']<1100) &
(df['expected_recovery_amount']>=900)]['recovery_strategy'],
df['sex'])
>>> print(crosstab)
...| sex | Female | Male |
|---|---|---|
| recovery_strategy | ||
| Level 0 Recovery | 32 | 57 |
| Level 1 Recovery | 39 | 55 |
# Chi-square test
chi2_stat, p_val, dof, ex = stats.chi2_contingency(crosstab)
>>> print(p_val)
... 0.5377947810444592Â Â We are now reasonably confident that customers just above and just below the $1000 threshold are, on average, similar in their average age and the percentage that are male.
  It is now time to focus on the key outcome of interest, the actual recovery amoun
  Let's make a scatter plot of Expected Recovery Amount (X)
versus Actual Recovery Amount (Y) for Expected Recovery
Amounts between $900 to $1100. This range covers Levels 0 and 1.
A key question is whether or not we see a discontinuity (jump) around the $1000 threshold.
plt.scatter(x=df['expected_recovery_amount'], y=df['actual_recovery_amount'], c="g", s=2)
plt.xlim(900, 1100)
plt.ylim(0, 2000)
plt.show()
  As we did with age, we can perform statistical tests to see if the actual recovery amount has a discontinuity above the $1000 threshold.
We will use the Kruskal-Wallis test, again.We will repeat the steps for a smaller window of $950 to $1050.
by_recovery_strategy['actual_recovery_amount'].describe().unstack()
Level_0_actual = era_900_1100.loc[df['recovery_strategy']=='Level 0 Recovery']['actual_recovery_amount']
Level_1_actual = era_900_1100.loc[df['recovery_strategy']=='Level 1 Recovery']['actual_recovery_amount']
>>> print(stats.kruskal(Level_0_actual, Level_1_actual))
... KruskalResult(statistic=65.37966302528878, pvalue=6.177308752803109e-16)
# Repeat for a smaller range of $950 to $1050
era_950_1050 = df.loc[(df['expected_recovery_amount']<1050) &
(df['expected_recovery_amount']>=950)]
Level_0_actual = era_950_1050.loc[df['recovery_strategy']=='Level 0 Recovery']['actual_recovery_amount']
Level_1_actual = era_950_1050.loc[df['recovery_strategy']=='Level 1 Recovery']['actual_recovery_amount']
>>>print(stats.kruskal(Level_0_actual, Level_1_actual))
... KruskalResult(statistic=30.246000000000038, pvalue=3.80575314300276e-08)Â Â We now want to take a regression-based approach to estimate the program impact at the $1000 threshold using data that is just above and below the threshold.
import statsmodels.api as sm
X = era_900_1100.expected_recovery_amount
y = era_900_1100.actual_recovery_amount
X = sm.add_constant(X)
model = sm.OLS(y, X).fit()
predictions = model.predict(X)
>>> print(model.summary())
... OLS Regression Results
==================================================================================
Dep. Variable: actual_recovery_amount R-squared: 0.261
Model: OLS Adj. R-squared: 0.256
Method: Least Squares F-statistic: 63.78
Date: Thu, 20 May 2021 Prob (F-statistic): 1.56e-13
Time: 12:30:07 Log-Likelihood: -1278.9
No. Observations: 183 AIC: 2562.
Df Residuals: 181 BIC: 2568.
Df Model: 1
Covariance Type: nonrobust
============================================================================================
coef std err t P>|t| [0.025 0.975]
--------------------------------------------------------------------------------------------
const -1978.7597 347.741 -5.690 0.000 -2664.907 -1292.612
expected_recovery_amount 2.7577 0.345 7.986 0.000 2.076 3.439
==============================================================================
Omnibus: 64.493 Durbin-Watson: 1.777
Prob(Omnibus): 0.000 Jarque-Bera (JB): 185.818
Skew: 1.463 Prob(JB): 4.47e-41
Kurtosis: 6.977 Cond. No. 1.80e+04
==============================================================================
  From the first model, we see that the expected recovery amount's
regression coefficient is statistically significant.
The second model adds an indicator of the
true threshold to the model (in this case at $1000).
If the higher recovery strategy helped recovery more money,
then the regression coefficient of the true threshold will be greater than zero.
If the higher recovery strategy did not help recovery more money, then the regression
coefficient will not be statistically significant.
# Create indicator (0 or 1) for expected recovery amount >= $1000
df['indicator_1000'] = np.where(df['expected_recovery_amount']<1000, 0, 1)
era_900_1100 = df.loc[(df['expected_recovery_amount']<1100) &
(df['expected_recovery_amount']>=900)]
X = era_900_1100[['expected_recovery_amount','indicator_1000']]
y = era_900_1100.actual_recovery_amount
X = sm.add_constant(X)
model = sm.OLS(y,X).fit()
>>> print(model.summary())
...OLS Regression Results
==================================================================================
Dep. Variable: actual_recovery_amount R-squared: 0.314
Model: OLS Adj. R-squared: 0.307
Method: Least Squares F-statistic: 41.22
Date: Thu, 20 May 2021 Prob (F-statistic): 1.83e-15
Time: 12:30:07 Log-Likelihood: -1272.0
No. Observations: 183 AIC: 2550.
Df Residuals: 180 BIC: 2560.
Df Model: 2
Covariance Type: nonrobust
============================================================================================
coef std err t P>|t| [0.025 0.975]
--------------------------------------------------------------------------------------------
const 3.3440 626.274 0.005 0.996 -1232.440 1239.128
expected_recovery_amount 0.6430 0.655 0.981 0.328 -0.650 1.936
indicator_1000 277.6344 74.043 3.750 0.000 131.530 423.739
==============================================================================
Omnibus: 65.977 Durbin-Watson: 1.906
Prob(Omnibus): 0.000 Jarque-Bera (JB): 186.537
Skew: 1.510 Prob(JB): 3.12e-41
Kurtosis: 6.917 Cond. No. 3.37e+04
==============================================================================
  The regression coefficient for the true threshold was
statistically significant with an estimated impact of around $278.
This is much larger than the $50 per customer needed to run this higher recovery strategy.
Whether we use a wide ($900 to $1100) or narrower window ($950 to $1050),
the incremental recovery amount at the higher recovery strategy is much
greater than the $50 per customer it costs for the higher recovery strategy.
So we conclude that the higher recovery strategy is worth the
extra cost of $50 per customer.
era_950_1050 = df.loc[(df['expected_recovery_amount']<1050) &
(df['expected_recovery_amount']>=950)]
X = era_950_1050[['expected_recovery_amount','indicator_1000']]
y = era_950_1050['actual_recovery_amount']
X = sm.add_constant(X)
model = sm.OLS(y,X).fit()
>>> model.summary()
...OLS Regression Results Dep. Variable: actual_recovery_amount R-squared: 0.283 Model: OLS Adj. R-squared: 0.269 Method: Least Squares F-statistic: 18.99 Date: Thu, 20 May 2021 Prob (F-statistic): 1.12e-07 Time: 12:30:07 Log-Likelihood: -692.92 No. Observations: 99 AIC: 1392. Df Residuals: 96 BIC: 1400. Df Model: 2 Covariance Type: nonrobust coef std err t P>|t| [0.025 0.975] const -279.5243 1840.707 -0.152 0.880 -3933.298 3374.250 expected_recovery_amount 0.9189 1.886 0.487 0.627 -2.825 4.663 indicator_1000 286.5337 111.352 2.573 0.012 65.502 507.566 Omnibus: 39.302 Durbin-Watson: 1.955 Prob(Omnibus): 0.000 Jarque-Bera (JB): 82.258 Skew: 1.564 Prob(JB): 1.37e-18 Kurtosis: 6.186 Cond. No. 6.81e+04