Predictive Modeling for Market Risk in the Banking Book
Transcript of Predictive Modeling for Market Risk in the Banking Book
Predictive Modeling for Market Risk in the Banking Book
4EK614
Applied Operational Research in Business Consulting
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With You Today
Predictive Modeling for Market Risk in the Banking Book
Tomáš SobotkaSenior Manager in Market Risk Team
Branislav Lovás
Senior Consultant in Market Risk Team
Market Risk & Regulatory Team
Quantitative Services
ALM
Treasury
Regulatory
Model Development
Model Validation
Securities Valuations
Derivatives Valuations
Data Analysis
Data Mining
Investment RoboAdvisors
Behavioral Modelling
Stress Testing
Forecasting
Regulatory Reporting
Methodological Review
Our projects
Our services
Eliška Kompanová
Senior Consultant in Market Risk Team
Adéla Nguyenová
Consultant in Market Risk Team
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Housekeeping:
1. Basic understanding of statistical and mathematical concepts(mathematical modelling, time series)
2. Elementary knowledge of programming (Python, R, VBA)
Please see Annex to links with helpful sources.
Prerequisites
Day 1: Credit RiskDay 2: Market RiskClassroom: OnlineTime: 9:15am – 10:45am
11:00am – 12:30pm
Course Structure
Please note that you are not limited to methods presented today (and it is more than welcomed to new approaches)Non-Maturity Deposit Modelling1. Case study – you will obtain dataset for modelling balance of non-maturity deposits. Your task will be to analyze the dataset, split it to train set and test set. With train dataset, you will develop selected model for non-maturity deposit balances. Then you will take your test dataset and see how your model performs.2. Outputs – PPT presentation or PDF, summarizing the abovementioned outputs, and scripts in Python, R or VBA (including the spreadsheet) that were used. Please send these outputs to [email protected]. Submission deadline: 7 May 20213. Output presentation for EY (most important!)– short (10-15 minutes) presentation + Q&A about results of this assessment; the presentation will be delivered online and will take place during the week starting from 10 May 2021.
Course Assessment
1. PowerPoint slides, provided after the course
2. Jupyter notebook *.ipynb files, provided after the course
Study materials
Predictive Modeling for Market Risk in the Banking Book
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Contents
Predictive Modeling for Market Risk in the Banking Book
1. Mathematical Crash Course
I. Somewhat Heuristic Introduction to Probability and
Stochastic Processes
II. Time Series Modelling
III. Linear Regression
2. Behavioral modelling in the Banking Book
I. Introduction to the Banking Book
II. Behavioral models
3 Non-Maturity Deposit modelling
I. Segmentation
II. Liquidity modeling of NMD
III. IR sensitivity models – β and optimal portfolio approach
IV. Other issues
4 Hands-on Case Study: Instructions for Module Assignments
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Mathematical Crash Course
Somewhat Heuristic Introduction to Probability and Stochastic Processes
Time Series Modelling
Linear Regression
1
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Questions 1: Basic Demographics
Predictive Modeling for Market Risk in the Banking Book
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Probability Space
• Key object is a so-called probability space, which is a triplet (Ω, ℱ, 𝑃):
• Ω: Sample space (contains all possible outcomes)
• ℱ: 𝜎 –algebra on Ω, (contains all events we are interested in) i.e.:
• Ω ∈ ℱ
• If 𝐴1, 𝐴2… ∈ ℱ then ڂ𝑖=1+∞ 𝐴𝑖 ∈ ℱ
• If A ∈ ℱ then 𝐴𝐶 = Ω − 𝐴 ∈ ℱ
• 𝑃 – probability measure, i.e. a set function 𝑃:Ω ↦ [0, 1]:
• 𝑃 ∅ = 0; 𝑃 Ω = 1
• For pairwise disjoint sets Ai ∈ ℱ: 𝑃 𝑖=1ڂ+∞ 𝐴𝑖 = σ𝑖=1
+∞ 𝑃(𝐴𝑖)
• The above might sound theoretical, but the triplet is a cornerstone of any stochastic modelling
• Additionally, we might consider a filtered probability space (Ω, ℱ, ℱ𝑡 𝑡≥0, 𝑃) where ℱ𝑡 𝑡≥0 is an increasing set of sub-𝜎-
algebras ⊂ ℱ
Example:
• Rolling dice – what would be Ω?
• What is the smallest ℱ?
• What if we want to know what is the probability of casting an odd / even number?
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Probability – Conditioning & Independence
• Assuming probability space Ω,ℱ, 𝑃 and two events 𝐴, 𝐵 ∈ ℱ
Conditional probability:
• 𝑃 𝐴 𝐵 =𝑃(𝐴 ∩ 𝐵)
𝑃(𝐵)≈ “probability of event A occurring if event B occurs”
Independence of two events:
• Two events 𝐴, 𝐵 ∈ ℱ are said to be independent if:
• 𝑃 𝐴 ∩ 𝐵 = 𝑃 𝐴 𝑃(𝐵)
Example:
• Rolling dice
• What is probability of 𝐴 = {1}conditional on B = {1,3,5}?
• What is a conditional probability of two independent events?
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Questions 2: Roll a Dice
Predictive Modeling for Market Risk in the Banking Book
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Random Variables
• Real-valued random variable is defined as 𝑋:Ω ↦ ℝ
• For math nerds: 𝑋 is a measurable function on Ω,ℱ, 𝑃
Technically:
• We denote,𝑋 = 𝑥 = 𝜔 ∈ Ω: 𝑋 𝜔 = 𝑥𝑋 < 𝑥 = 𝜔 ∈ Ω: 𝑋 𝜔 < 𝑥
𝑎 < 𝑋 < 𝑏 = 𝜔 ∈ Ω: 𝑎 < 𝑋 𝜔 < 𝑏
• Analogously, random variables 𝑋1, 𝑋2 are independent if for all 𝑥1, 𝑥2:
𝑃 𝑋1 = 𝑥1; 𝑋2 = 𝑥2 = 𝑃 𝑋1 = 𝑥1 𝑃(𝑋2 = 𝑥2)
Examples:
• Rolling dice
• 2 dice rolled at once, 𝑋 is the sum of casted values on dice
• Identity function
• Coin tossing bet
• Random walk of a drunk
Realization of 𝜔 ∈ Ω
𝜔 = H
𝜔 = T
$100
$0
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Cumulative distribution function
• Let 𝑋 be a real-valued (continuous) random variable on Ω,ℱ, 𝑃 , then 𝐹 𝑥 : 𝐹 𝑥 = 𝑃 𝑋 ≤ 𝑥 =
∞−𝑥
𝑓𝑋 𝑠 𝑑𝑠, where
• 𝐹 𝑥 is the cumulative distribution function (CDF)
• 𝑓𝑋(𝑥) is the probability density function (PDF), (probability mass function for discrete random variables)
• The CDF:
• ranges from 0 to 1,
• is an increasing function,
• is right-continuous.
Predictive Modeling for Market Risk in the Banking Book
Useful Functions: CDF & PDF
Continuous random variableDiscrete random variable
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• The normal distribution is bell-shaped, entirely defined by two parameters
• Mean - 𝜇
• Standard deviation - 𝜎
• The normal PDF can be analytically expressed:
Predictive Modeling for Market Risk in the Banking Book
Important Example: Normal Distribution
𝑓 𝑥 =1
𝜎 2𝜋𝑒–(𝑥–𝜇)2
2𝜎2
• Why is this important?
-0,3 -0,2 -0,1 0 0,1 0,2 0,3
Standard normal distribution
• The standard normal distribution has 𝜇 = 0 and 𝜎 = 1
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Questions 3: Other probability distribution functions
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Stochastic (random) process
• Let 𝜏 be a subset of [0, +∞], then a family of random variables indexed by 𝜏: 𝑋𝑡 𝑡∈𝜏 is a stochastic process. Two basic observations (for real-values stochastic processes):
• 𝑋𝑡 𝜔 : 𝜏 ↦ ℝ for a fixed 𝜔 is a sample path (or trajectory)
• 𝑋𝑡 𝜔 :Ω ↦ ℝ for a fixed 𝑡 is a random variable
Example – constructing a “Random Walk” model
• A simple random walk process 𝑋𝑛 𝑛∈ℕ0 can be constructed:
1. 𝑋0 = 0
2. Increment 𝑋𝑛+1 − 𝑋𝑛 is independent of all previous increments
3. Increment 𝑋𝑛+1 − 𝑋𝑛 has a coin toss distribution (binomial):
𝑃 𝑋𝑛+1 − 𝑋𝑛 = +1 = 𝑃 𝑋𝑛+1 − 𝑋𝑛 = −1 =1
2
Predictive Modeling for Market Risk in the Banking Book
Stochastic processes - Intro
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• Stochastic time-series is a sequence of data collected at specified time points 𝑡1, 𝑡2, 𝑡3, …
• Trend, seasonality, cyclicity, irregularity
ARIMA(p,q): 𝑋𝑡 − 𝛼𝑋𝑡−1 −⋯− 𝛼𝑝𝑋𝑡−𝑝 = 𝜖𝑡 + 𝜃1𝜖𝑡−1 +⋯+ 𝜃𝑞𝜖𝑡−𝑞
• Auto regressive integrated moving average
• Three main parameters:
• p – number of autoregressive terms (AR) … current value as a linear combination of past values
• d – non-seasonal differences to achieve stationarity (I)
• q – number of lagged forecast errors in the prediction equation (MA) … current error as a linear combination of past errors
Generalized GBM
Stochastic time-series models
Predictive Modeling for Market Risk in the Banking Book
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• Linear approach to modeling a relationship between one dependent variable (outcome) and multiple independent variables(inputs)
𝑦 = 𝑥𝑇𝛽
• Linearity
• Normality – errors have normal distribution
• Homoscedasticity – same variance
• Independence of observations
• Lack of perfect multicollinearity
• MLE:
𝑌 = (𝑋𝑇𝑋)−1𝑋𝑇𝑌
Linear Regression
Predictive Modeling for Market Risk in the Banking Book
y
x
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Questions 4: Other models
Predictive Modeling for Market Risk in the Banking Book
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Behavioral modelling in the Banking Book2
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Key products offered by banks
Assets
Retail segmentPersonal loans
Mortgage (various types)
Debt consolidation
Overdrafts
Credit cards
SME segmentCommercial loans - secured/unsecured
Corporate segmentInvestment loans
Working capital loans
Liabilities
Across all segmentsCurrent accounts
Savings accounts
Term deposits (single/revolving)
Structured deposits (embedded options)
Bonds
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Role of a Typical Commercial Bank
Predictive Modeling for Market Risk in the Banking Book
Deposits
Other Borrowing (Wholesale)
CapitalFixed Assets
Liquid Assets
Loans & Advances
Assets Liabilities
‘Typical’ Balance Sheet Role of Maturity Transformation
De
po
sit
Lo
an
He
dg
e
Ass
et
He
dg
e
Lia
bili
ty
Time
Banks play an important role as an intermediary in the financial system. They typically have two main functions:1. Take on deposits from the public (typically ‘short term’ in nature)
2. Lend out loans / mortgages (typically ‘long term’ in nature)
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• Banking Book assets and liabilities are those which are intended to be held on the balance sheet until
maturity at amortized value.
• The banking book can also include those derivatives that are used to hedge exposures arising from the
banking book activity, including interest rate risk.
Banking Book
Predictive Modeling for Market Risk in the Banking Book
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• In order to match assets and liabilities with the same interest
rate profile, banks need to know the maturity (re-price) date of
those assets and liabilities.
• The following assets and liabilities are often associated with
customer optionality and therefore the maturity is not clear:
Behavioral Models
Predictive Modeling for Market Risk in the Banking Book
Psychology
Decision-making
Finance / economics
Behavioral finance
Product Type Optionality
Fixed Term Loan Customers may have the option to re-pay the loan earlier than its maturity/reprice date
Fixed Term Deposit Customers may have the option to withdraw deposits earlier than the fixed term or to top-up deposits at the original fixed term rate
Non-Maturity Deposit There is no stated maturity but customers have the option to withdraw at any time
Pipeline Banks need to take a view on assets/liabilities which are contractual but have not hit the balance sheet yet.
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Behavioral Models
Predictive Modeling for Market Risk in the Banking Book
Banks employ a number of techniques to assess the likely behaviour of these balances in order to match assets and liabilities of the same interest rate profile:
1. Fixed rate products with pre-payment / early withdrawal / top up optionality
2. Non-maturing deposits
Determined using
statistical modelling of behaviours
under different scenarios
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• Market
• interbank and governments
• Macro-economic
• inflation, economic growth
• Behavioral
• reaction of customers to the market (withdrawing, saving, …)
• Personal
• Age, education, job, ..
Predictive Modeling for Market Risk in the Banking Book
Behavioral Models – input data types
What Risks are in the Banking Book?
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Non-Maturity Deposit modelling3
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Questions 5: Non-maturity deposits
Predictive Modeling for Market Risk in the Banking Book
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• Liabilities in the Banking book
• Depositors can withdraw their funds at any time without any penalty
• Interest rates are unilaterally set up by the Bank
• One of the most stable sources of funding for banks; asset
• Contractual maturity – overnight (in reality significant effective duration)
• Retail savings, money-market accounts
• Modelling this early redemption option is very challenging
• NMD balances can be modelled under 3 different assumptions:
• Run-off
• Static balance-sheet
• Assuming inflow of new clients
• Factors affecting NMD:
• Market (interbank and governments)
• Macro-economic (inflation, economic growth)
• Behavioral (reaction of customers to the market)
► Main components discussed:
a) Liquidity runoff model / balances prediction
b) IR sensitivity model (replication portfolio)
Non-maturity deposits
Predictive Modeling for Market Risk in the Banking Book
Liquidity risk
management
Interest rate
risk / ALM
FTP
a) Liquidity runoff model
b) IR sensitivity model
c) Floor add-on
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2.1 Modelling of NMD: Segmentation
Predictive Modeling for Market Risk in the Banking Book
► The first step in the deposit characterization process is to divide demand deposits into segments, which is criticalfor an accurate analysis.
► The main goal of product segmentation is to find homogeneous enough segments, while ensuring a minimumthreshold of materiality and simplicity.
► The segmentation process tries to reach a balance between three ideals:
► Typical segmentation criteria are:
1) Product type: Completely different products should not be examined together
2) Currency: Products with different currencies should not be pooled together.
► Segmentation process requires deep knowledge on the specifics, management strategy and historical behavior ofthe products.
Homogenity
SimplicityMateriality
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2.2 Liquidity modelling of NMD: Overview
Predictive Modeling for Market Risk in the Banking Book
Overview
► A blend of quantifiable
statistical models coupled
with business adjustments
► Good segmentation of the
products is essential
Modelling approaches
► Segmentation based
on various factors, e.g.
currency, product time,
country, type of origination
(on-line / branch)
► Two types of statistical
models (in practice,
combination of both is used)
(next slides)
Model goal
► Assign a runoff profile
to deposit products
► The profiles should be
consistent with the historical
behaviour of the deposits
according to prevailing
market conditions
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2.2 Liquidity modelling of NMD: Run-off profile
Predictive Modeling for Market Risk in the Banking Book
Stochastic time-series models
(ARIMA, generalized GBM)
► Modelling deposit balances evolution:
1. Runoff profile as an confidence interval of the fitted model (excl. new production)
2. Prediction of balances (including new production) expressed as expected value of the balance conditional on
current information – evaluated by:
I. Analytic expression (we know how to express this e.g. for GBM)
II. By Monte Carlo simulation
► Seasonality typically taken into account
► Statistical testing in place to validate appropriateness of the model
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2.2 Liquidity modelling of NMD: Core volume and vintage analyses
Predictive Modeling for Market Risk in the Banking Book
► Balance volatility model determines what level of balances
will remain with the bank in the long term given a level of
confidence.
► As an output, balance volatility model divides the balances
into two portions:
► Core balances which remain with the bank under almost
all market conditions
► Non-core balances which fluctuate over time due to
market and idiosyncratic reasons and are typically
characterized as short term.
► The analysis of core vs. non-core balances is performed
through a growth based regression model.
► Balance volatility model fits the product balances to trend
models (exponential, linear or logarithmic) and find the
variation of actual balances around the trend line.
7 000
8 000
9 000
10 000
11 000
12 000
13 000
14 000
15 000
I-06 VII-06 I-07 VII-07 I-08 VII-08 I-09 VII-09 I-10 VII-10
Bala
nce
Months
Core balance Balance development Linear fit
Step 1: Fit the trend line
Step 2: Measure variation from the trend
Step 3: Determine the core portion
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- 10 20 30 40 50 60
Rem
ain
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bala
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in %
Months
Product run-off profile
Jan 2006 Feb 2006 Mar 2006 Apr 2006
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2.2 Liquidity modelling of NMD: Challenges and Market practices highlights
Predictive Modeling for Market Risk in the Banking Book
Challenges
► To distinguish between seasonal outflows and surge outflows (due to environmental
changes)
► Lack of historical balance data to support the granular segmentation analytics
► Difficult to have statistically sound models of type 1. for all products
► One might need to switch to a simpler expert model instead
► Good model governance is key here
Market practices highlights
► Hypothesis testing for confidence interval reliability
► Concentration risk
► Average account balance vs # accounts
► Seasonality & surge balance adjustments
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2.3 IR sensitivity models – β and portfolio optimization: Overview
Predictive Modeling for Market Risk in the Banking Book
Overview
► As previously, a blend of
quantifiable statistical models and
expert adjustments is put in place
► Adjustments should align for
forward looking expectations on
rates and for business rationale
► Main output of the model –
replication portfolio
Modelling
approaches
► Two main concepts
are utilized,
sometimes they are
combined together
(i.e. via cointegration
analysis)
Model goal
► To stabilize NII and
to ensure correct
inputs for FTP
mechanisms
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2.3 Modelling of NMD: Rate sensitivity analysis
Predictive Modeling for Market Risk in the Banking Book
► Characterization of administered rates for deposit products describes the significance of market rate changes on the rates paid by bank to thecustomer.
► By modeling the behavior of interest rates paid relative to market rates, a better understanding of repricing behavior and the sensitivity ofinterest expenses to market rates can be gained.
► The interest rate paid to indeterminate maturity products’ depositors is typically a combination of one or more market rates, and fixedcomponent.
► In order to determine which of market ratesexplain the changes in the rates paid by thebank, a multiple regressions are made.
► Coefficients of this regression equation tellwhat percentage of the portfolio reprices withthe associated market rate.
Δproduct rate = 40% Δ 1M PRIBOR
► This repricing behavior indicates that 40% ofthe portfolio reprices with the 1M PRIBOR,while the remaining 60% of the portfolio is rateinsensitive.
0,5%
1,0%
1,5%
2,0%
2,5%
3,0%
3,5%
4,0%
4,5%
5,0%
Inte
rest
ra
te
Months
Interest rate development
Product rate 1M PRIBOR 3M PRIBOR
6M PRIBOR 12M PRIBOR
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2. β – rate sensitivity models
► Provide assumptions on how big change in interest rates one can pass to specific
client categories
► Beta (β) represents a deposit elasticity to changes in interest rates
► Retail NMD typically exhibit lower β compared to Wholesale deposits and savings
accounts
► Short-term/Long-term β and Linear /Dynamic β choices typically considered
2.3 IR sensitivity models – β and portfolio optimization: Modelling approaches
Predictive Modeling for Market Risk in the Banking Book
Typical utility functions
Criterion Optimisation goal
Volatility of the margin Minimize
Correlation between
customer and market ratesMaximize
Sharpe ratio Maximize
Typical β models
Model Description
Linear rate modelChange in rates proportional to the
benchmark
Mean reverting equilibrium
modelChanges due to short- and long-term effects
Direction dependent rate
model
Different sensitivity to increases and
decreases of the benchmark
Level dependent rate modelDifferent sensitivities when benchmark rates
are low / high
1. Portfolio optimization
► Typically connected with liquidity runoff (as
an upper bound or target) and regulatory
requirements
► One tries to find a portfolio of market
instruments that would have led to optimal
utility function value over relevant historical
time frame
► One might consider more than one criterion
(Sharpe, margin stability, duration, impact
under stress scenario)
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2.3 IR sensitivity models – β and portfolio optimization: Modelling approaches
Predictive Modeling for Market Risk in the Banking Book
Short term β Long term β
► Influenced by tactical
pricing expectations, line of
business Judgment, and
acute historical experience
► Influenced by statistically determined
historical experience (long term), and
business judgement.
► Reflects deposit rate paid in equilibrium
► Constant recalibration and
back-testing
► Less frequent back-testing
Dynamic β Linear β
► Reflects the changing sensitivity of
customer rates depending on the level
of interest rates as well as the relative
change in interest rate across the life
of the deposit
► A constant sensitivity of changes in
customer rates to changes in
interest rates
► Provides a better convexity measure
to the deposit profile
► Captures the asymmetrical behavior
as well as beta response to changes
in the level of rates
► Operationally easier
► Requires a less frequent update to
the hedging strategy
► Challenging operationally
► Difficult to apply to FTP
► Can be difficult to implement micro-
level hedging strategy
► Requires frequent beta assumption
review. Most common review
frequency range from 6-12 months
► Could be significantly off from the
spot beta at a given time, resulting
in disincentives
► Reduces transparency for the
Business
0,5%
1,0%
1,5%
2,0%
2,5%
3,0%
3,5%
4,0%
4,5%
5,0%
Inte
res
t ra
te
Interest rate development
Product rate
1M PRIBOR
3M PRIBOR
6M PRIBOR
12M PRIBOR
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2.3 IR sensitivity models – β and portfolio optimization: Challenges and Market practices highlights
Predictive Modeling for Market Risk in the Banking Book
Challenges
► What historical time-frame to use (e.g. short-term β vs long term
β), also applicable for portfolio optimization
► Manage operational complexity, especially for replicating
portfolio and dynamic β approaches
► Finding a correct segmentation of NMD volumes
Market practices highlights
► Portfolio optimization can be done by local optimizer with initial guess equal to previous
weight, or discrete steps
► Embedded floors taken into account:
a) Combination of β-Level and direction dependent rate models
b) via add-ons (incorporating value of IR floors)
c) or ignored
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2.4 Other issues
Predictive Modeling for Market Risk in the Banking Book
• Negative IR policy (NIRP) and embedded optionality
• FTP rate
• An all-in FTP rate for a deposit product is the sum of base rate, term liquidity premium, and a contingent liquidity
cost.
• New benchmark rates
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Questions 6: Your balance
Predictive Modeling for Market Risk in the Banking Book
0
500
1000
1500
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Balance 1
0
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600
800
1000
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Balance 2
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Balance 3
0
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Balance 4
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Questions 7: Modelling approaches
Predictive Modeling for Market Risk in the Banking Book
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Hands-on Case Study: Instructions for Module Assignments
4
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Practical Part – Jupyter Notebook
Predictive Modeling for Market Risk in the Banking Book
Freely available as part of Anaconda Distribution at: https://www.anaconda.com/distribution/
We use Python 3.7 version.
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Course Assessment
Predictive Modeling for Market Risk in the Banking Book
• Please note that you are not limited to methods presented today (and it is more than
welcomed to new approaches)
• Non-Maturity Deposit Modelling
• 1. Case study – you will obtain dataset for modelling balance of non-maturity deposits. Your
task will be to analyze the dataset, split it to train set and test set. With train dataset, you will
develop selected model for non-maturity deposit balances. Then you will take your test dataset
and see how your model performs.
• 2. Outputs – PPT presentation or PDF, summarizing the abovementioned outputs, and scripts
in Python, R or VBA (including the spreadsheet) that were used. Please send these outputs to
[email protected]. Submission deadline: 7 May 2021
• 3. Output presentation to the Bank Board – short (10-15 minutes) presentation about results of
this assessment; the presentation will be delivered online. Presentations will take place during
week starting from 10 May 2021.
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Course Assessment – structure of the presentation
Predictive Modeling for Market Risk in the Banking Book
1. Data description and model selection
2. Brief model description
3. How your model performs (make prediction for the fourth year and compare the prediction
with the real values)
4. Summarize your results
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Course Assessment – evaluation
Predictive Modeling for Market Risk in the Banking Book
• You will present your results to the Bank Board (four of us)
• What will be important for us?
1. The quality of your presentation and deliverables
2. The quality of your model (assumptions, errors, ..)
3. The innovation
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Annex + Q&A5
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• The mathematical optimization (also known as mathematical programming) forms a cornerstone of quantitativeportfolio optimization; it can be described as a process of looking for the extreme of a function (maximum orminimum).
• Apart from asset allocation, optimization has many uses in quantitative finance – model calibration, financialderivates pricing or asset-liability management.
• Optimization problem can be summarized by three components:
and can be formally written as:
Optimization (1)
Predictive Modeling for Market Risk in the Banking Book
Optimization problem component Asset allocation application
Objective function 𝑓(𝑥)Portfolio risk as a function of portfolio
weights, e.g. portfolio volatility 𝑤𝑇Σ𝑤
Vector of control variables 𝑥 Vector of portfolio weights 𝑤
Constraints set ℂ Portfolio weights must add up to 100%
min𝑤∈ℂ
𝑓(𝑥)
𝑠. 𝑡. ℂ: 𝑔𝑖 𝒙 ≤ 0 𝑖 = 1,… , 𝐼 (inequality constraints)ℎ𝑗 𝒙 = 0 𝑗 = 1,… , 𝐽 (equality constraints)
(25)
Useful optimization property: max𝑓 𝑥 = min−𝑓 𝑥
Page 49
• There are two types of function extremes:
• Local (maxima/minima) – extreme of the function in the neighborhood offeasible solutions.
• Global (maxima/minima) – extreme of the function in the set of all feasiblesolutions.
• The characteristics of the optimization problem (also referred to asmathematical programs) components of the determine its type, e.g.linear objective function with linear constrains form a linearprogram, a quadratic objective function with linear constraints leadsto quadratic program. Individual types of optimization problemshave their properties which can be usually exploited – e.g. in case ofconvex programs all local extremes are also global ones.
• Some of the optimization problems can be solved analytically withthe help of matrix algebra (e.g. portfolio variance minimization withequality constraints) but majority of problems require numerical,iterative algorithms, for example Newton-type methods such assteepest descent.
Optimization (2)
Predictive Modeling for Market Risk in the Banking Book
Global maximum
Local maxima
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