fixed income research for institutional client use only

22
DISCLOSURE APPENDIX AT THE BACK OF THIS REPORT CONTAINS IMPORTANT DISCLOSURES AND ANALYST CERTIFICATIONS. CREDIT SUISSE SECURITIES RESEARCH & ANALYTICS BEYOND INFORMATION ® Client-Driven Solutions, Insights, and Access Modeling and Analytics Measuring MBS curve risk with Implied Mortgage Rate Sensitivity (“IMS”) approach Backtesting model hedge ratios and “trader durations” OAS models often produce questionable partial duration profiles, and thus reduce their usefulness in measuring and managing MBS curve risk. These are usually caused by idiosyncratic features in the embedded mortgage rate models. The Implied Mortgage Rate Sensitivity (“IMS”) is a Credit Suisse proprietary methodology for mortgage rates modeling and for computing MBS partial durations. We show how it can be used to consistently model MBS curve risk across maturities and product types. Back test results are analyzed to account for additional risk factors of supply/demand shocks due to QE programs and high model risk for high premium coupons. Comparisons between model hedge ratios and “trader durations” show they are generally consistent once the shape of yield curve volatility and OAS directionality are taken into account. Mathematical formula for the IMS method are listed in the appendix for our modeling peers who may wish to replicate it themselves. Research Analysts David Zhang 212 325 2783 [email protected] Joy Zhang 212 325 5702 [email protected] Yihai Yu 212 325 7922 [email protected] 01 December 2014 Fixed Income Research http://www.credit-suisse.com/researchandanalytics FOR INSTITUTIONAL CLIENT USE ONLY

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Page 1: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

DISCLOSURE APPENDIX AT THE BACK OF THIS REPORT CONTAINS IMPORTANT DISCLOSURES AND

ANALYST CERTIFICATIONS.

CREDIT SUISSE SECURITIES RESEARCH & ANALYTICS BEYOND INFORMATION®

Client-Driven Solutions, Insights, and Access

Modeling and Analytics

Measuring MBS curve risk with Implied

Mortgage Rate Sensitivity (“IMS”) approach

Backtesting model hedge ratios and “trader durations”

OAS models often produce questionable partial duration profiles, and thus

reduce their usefulness in measuring and managing MBS curve risk. These are

usually caused by idiosyncratic features in the embedded mortgage rate

models. The Implied Mortgage Rate Sensitivity (“IMS”) is a Credit Suisse

proprietary methodology for mortgage rates modeling and for computing MBS

partial durations. We show how it can be used to consistently model MBS curve

risk across maturities and product types. Back test results are analyzed to

account for additional risk factors of supply/demand shocks due to QE programs

and high model risk for high premium coupons. Comparisons between model

hedge ratios and “trader durations” show they are generally consistent once the

shape of yield curve volatility and OAS directionality are taken into account.

Mathematical formula for the IMS method are listed in the appendix for our

modeling peers who may wish to replicate it themselves.

Research Analysts

David Zhang

212 325 2783

[email protected]

Joy Zhang

212 325 5702

[email protected]

Yihai Yu

212 325 7922

[email protected]

01 December 2014

Fixed Income Research

http://www.credit-suisse.com/researchandanalytics

FOR INSTITUTIONAL CLIENT USE ONLY

Page 2: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 2

MBS partial durations from OAS models - impact of mortgage rate modeling choices

With the ongoing yield curve volatility amid uncertainties in monetary policy, investors

have inquired about MBS curve risk and Locus model partial durations. We have

developed a proprietary methodology at Credit Suisse, the “implied mortgage rate

sensitivity” (“IMS”) approach, to compute MBS durations and partial durations, and to

project future mortgage rates in the OAS model. We share this methodology here and

discuss its applications in MBS valuation and hedging.

In the Option-Adjusted-Spread (OAS) model framework, computing partial durations

involves shocking the spot yield curve as well as shocking the spot mortgage rate

simultaneously, to compute the sensitivities of model prices. Typically, the amount of

mortgage rate shock associated with that particular yield curve shock is determined by the

embedded mortgage rate model. The embedded mortgage rate model can be driven by

discrete yield curve points or by the whole yield curve (or in certain hybrid forms, as in the

Credit Suisse model). In this article, we use “mortgage rates” and “current coupon yield”

(“cc”) interchangeably, with the understanding that the mortgage rates are modeled

through the cc.

Early implementation of the discrete yield points based cc model (“discrete cc model”)

often uses just a 10yr point, i.e., cc = spread + 10yr swap/treasury yield (“10yr cc model”).

The Credit Suisse production model uses a nonlinear mix of 2/5/10 year swap yields

(“2/5/10 yr cc model”). The advantages of this approach are simplicity and computational

efficiency. The disadvantages are the arbitrariness of the modeling choices in both the

specific maturities and the weights (“loadings”) assigned to these maturities. The weight or

“loading” is the sensitivity of cc to a change in yield for that specific maturity. For example,

for a hypothetical mortgage rate model based on 2 and 10yr swap rates, cc = spread +

25% 2yr swap yield + 75% 10yr swap yield, the 25% and 75% are the weights or loadings

for the 2yr and 10yr maturities.

Exhibit 1: Example of unreasonable kinks in partial duration profile, due to arbitrarily choosing certain discrete swap terms in the cc model

Partial durations profile for FNCL 4.5 as of 2/21/2014 Partial duration profile for FNCL 6 as of 2/21/2014

Source: Credit Suisse

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production method 10Yr method

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production method 10Yr method

Page 3: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 3

Exhibit 1 shows the impact on the MBS partial duration profile due to the arbitrariness of

these modeling choices, by comparing the TBA partials between the Credit Suisse

production model (which uses a nonlinear combination of 2/5/10 year swap yields to drive

future mortgage rates) and a simple “10yr cc model”. The left diagram shows FNCL 4.5s

partials in the 1/2/3/4/5/6/7/8/9/10/15/30 year maturity grids.1 For the “10yr cc model”,

there are large differences between 9yr and 10yr partial durations. In fact, 9yr partial

duration is positive, while 10yr partial duration is negative. Obviously these results are

unreasonable, as one would expect similar partial durations between the neighboring 9yr

and 10yr points. This is because the “10yr cc model” drives mortgage rates exclusively

with the singular 10yr swap rates.

The right diagram of Exhibit 1 shows a similar issue for more sparse grids of 2/5/10/30 yr

partials. The “10yr cc model” shows a large negative partial profile for the 10yr sector while

30yr partial is close to be zero. For the “2/5/10 yr cc model”, the 10yr partial still shows a

negative “kink” versus the positive 5yr and 30yr partials. These contrasts between 10yr

and 30yr partials are due to the inclusion of the 10yr point and exclusion of the 30yr point

in the mortgage rates models. (the 30yr point is not included in our mortgage rate model

partly due to the high computation cost in projecting the 30yr swap rates in all future

scenarios. We will discuss this issue in detail later.) Obviously, partial duration profiles

(and, as a result, curve risk exposure measures) driven by these rather arbitrary modeling

features do not inspire confidence.

While it seems one way to reduce the “kinks” in the partial duration profile is to use more

maturity points on the yield curve to drive mortgage rates, modeling the weights/loadings

across the term structure may entail additional complexities. For example, how do we

determine weights for 2/5/10yr swap yields for mortgage rates in our production model and

why do we choose to use a nonlinear form? A common estimation approach is multiple

regression between historical data of mortgage rates/cc and swap yields of varying

maturities. In practice, regression approaches produce such wide ranges of values for

weights across maturities that the resulting curve risk exposures look arbitrary. The main

difficulties for the multiple regression approach are multicollinearity (yields are highly

correlated across maturities, making regression unstable) and model misspecification

(forcing linear regressions on a set of nonlinear relationships).

Whole curve mortgage rate models (“whole curve cc model”), on the other hand, utilize the

insight that the cc is the yield of a par mortgage pass-through bond. Hence, modeling

mortgage rates in an OAS framework becomes a self-reference mathematical problem2

The OAS model needs the embedded mortgage rate model to price MBS bonds, while the

mortgage rate model needs to price a par pass-through bond to solve the yield as cc.

While this method provides a consistent framework for the mortgage rate modeling, the

mathematical complexity of this approach often obscures the benefits it brings to MBS

valuation and risk management. For example, the backward induction method in this

framework is computationally expensive, but the differences in model OAS are usually

quite small, compared with a much simpler “10yr cc model”. 3

Based on the same insight, the Credit Suisse “implied mortgage rate sensitivity” (“IMS”)

methodology provides a practical and computationally economic approach for mortgage

rates modeling and for MBS partial durations. We show a simple example below to

illustrate the logic. The appendix lists the mathematical formula and some theoretical

discussions for our modeling peers who may wish to implement similar method.

1 Partial durations are generally computed in the context of a "grid" of maturities. Yield curve shock is a triangle that peaks at one

grid maturity, and diminishes at the two neighboring grid maturities.

2 For example, "The term Structure of Mortgage Rates: Citigroup's MOATS Model", Bhattacharjee and Hayre, Journal of Fixed Income, March 2006

3 For example, page 168-169, Andrew Davidson and Alexander Levin, "Mortgage Valuation Models, embedded options, risk, and uncertainty", 2014, Oxford University Press

Page 4: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 4

How to “imply” mortgage rate sensitivity to yield curve shocks?

Using the February 21, 2014 pricing day as an example, Exhibit 2 shows a base swap

curve, and a synthetic 30 year pass-through security, the “cc bond”, at par price, with a

coupon equal to the corresponding 30year current coupon yield of 3.3989% and a WAC

set at coupon+55.61bps. This 55.61bps spread is derived from interpolation of our WAC

assumptions for TBA 3s and 3.5s, which bracket the par cc bond. The “cc bond” is model

priced at 25.6bps OAS.

We show two examples of how much cc change is “implied”, given a 10bps increase in 5yr

swap yield. The first example shocks the 5yr rate by 10bps in the 2/5/10/30 year “grid”,

which leads to a triangle curve shock centered on the 5yr point and between the 2yr point

and 10yr point on the yield curve. In order to solve for the “implied” mortgage rate/cc

change due to the curve shock, we construct a new “cc bond” with the new current coupon

yield (to be solved for) as the bond coupon, and WAC at the same spread of 55.61bps to

the new cc. The new cc yield, 3.4137%, is solved by requiring the new “cc bond” to be

priced at par, under the same 25.6bps OAS. Hence the “implied” mortgage rate sensitivity

is 1.48bps for the 10bps 5yr yield shock.

The second example also uses a 10bps increase in 5yr swap yield, but in a finer “grid” of

1/2/3/….8/9/10/11/15/30 year points. Hence, the curve shock is a triangle centered with

10bps at the 5yr point and between the 4yr and 6yr points. This is a far smaller curve

shock than the previous 10bps 5yr swap yield shock in the 2/5/10/30 year “grid. As a result,

the “implied” mortgage rate sensitivity is only 0.39bps for the 10bps 5yr yield shock.

Note that in a “discrete cc model”, the mortgage rate shocks for the partial duration

computation do not take into account of the shape of the curve shock. Take the example

of a hypothetical mortgage rate model driven by linear combination of 2/5/10yr rates, and

assume cc = spread + 25% 2yr swap yield + 25% 5yr swap yield + 50% 10yr swap yield.

The mortgage rate sensitivities, used for partial duration computation, for our previous two

examples (10bps 5yr swap yield shock on 2/5/10/30 year grid and on

1/2/3/…./9/10/11/15/30 year grid) will be 25% for both, despite the fact that the second

curve shock is much smaller.

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01

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Exhibit 2: How to “imply” mortgage rate sensitivities to two examples of 10bps shocks to 5yr swap yield

February 21, 2014 pricing day

Source: Credit Suisse

Apply the same method to all other maturities for 1/2/3/…./9/10/11/15/30 year points, Exhibit 3 shows a sample result of “implied” mortgage rate sensitivities

(“IMS loadings”) across the yield curve. These IMS loadings are then used to compute partial durations across all MBS securities.

Exhibit 3: “Implied” mortgage rate sensitivities “IMS loadings” across a grid of yield points

February 21, 2014 pricing day

Term 1YR 2YR 3YR 4YR 5YR 6YR 7YR 8YR 9YR 10YR 15YR 30YR

dcc/dr 0.0065 0.0182 0.0292 0.0337 0.0395 0.0382 0.0371 0.0361 0.0471 0.1293 0.2269 0.1209

Source: Credit Suisse

We believe the IMS methodology provides a consistent framework for the mortgage rates sensitivities for partial duration curve shocks. This leads to

consistent and intuitive partial duration profiles, and, as an extension, sensible curve risk measures. Exhibit 4 shows the comparison between the IMS

partials and partials based on standard methodology, which we show in Exhibit 1. The IMS partials profiles are free of these issues identified in previous

sections.

Base curve 1M 3M 6M 1YR 2YR 3YR 5YR 7YR 10YR 20YR 30YR

Yield 0.158 0.238 0.243 0.265 0.449 0.821 1.639 2.256 2.831 3.528 3.665

Price OAS WAC

100 25.6 3.3989 3.9550

10 bps shock (5yr point in 2/5/10/30 grid)

1yr 2yr 3yr 4yr 5yr 6yr 7yr 8yr 9yr 10yr 15yr 30yr

Curve Shock 0 0 3.3 6.7 10 8 6 4 2 0 0 0

Price OAS WAC dCC

100 25.6 3.4137 3.9699 0.0148

10 bps shock (5yr point in 1/2/3/5/6/7/8/9/10/11/15/30 grid)

1yr 2yr 3yr 4yr 5yr 6yr 7yr 8yr 9yr 10yr 15yr 30yr

Curve Shock 0 0 0 0 10 0 0 0 0 0 0 0

Price OAS WAC dCC

100 25.6 3.4028 3.9590 0.0039New "cc bond" under new curve, solving for

coupon/WAC for the same oas at par price

New "cc bond" under new curve, solving for

coupon/WAC for the same oas at par price

Base case "cc bond" under base curve

Coupon/Mortgage rate

Coupon/Mortgage rate

Coupon/Mortgage rate

Page 6: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 6

Exhibit 4: Sensible and intuitive partials profile from the IMS method

Partials profile for FNCL 4.5 as of 2/21/2014 Partials profile for FNCL 6 as of 2/21/2014

Source: Credit Suisse

IMS captures nonlinear behaviors of mortgage rates

Profiles of the IMS loadings (sensitivities of mortgage rates to yield curve shocks) reveal

the nonlinear relationship between mortgage rates and swap rates, hence, the

shortcomings of linear mortgage rates models.

Exhibit 5 compares the IMS loadings for a 2/5/10/30 year grid for a steep and a flat yield

curve from 2014 and 2007. The loadings have much higher weightings for the front end of

the yield curve in a flat curve environment. This behavior is consistent with the mortgage call

options having a higher chance of earlier exercise given a flatter curve and lower forward

rates. A linear mortgage rates model produces constant loadings, and will not shift loadings

to the front end of yield curve as the curve flattens. As a result, it will overprice the call option

values, create artificial OAS tightening (positive OAS correlation with yield curve slope), and

its partial duration profile will be erroneously over-concentrated in the front.

Other factors responsible for the nonlinear relationships between mortgage rates and

swap yields include

− Yield level: higher yields/discount factors tend to shift the mortgage rates loading

to the front end of the curve, because the higher discount factors reduce the

present value of the back end cashflow in the mortgage pass-through.

-1

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0

0.5

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Term ( year )

production method10Yr methodIMS method

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2 5 10 30Term ( year )

production method

10Yr method

IMS method

Page 7: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 7

Exhibit 5: Flat yield curve tends to push the IMS loadings to the front of the yield curve

Left panel: Swap curves as of 2/21/2014( steep ) and 2/21/2007 (flat) IMS loadings (sensitivities of mortgage rate to swap rates shocks) for 2/5/10/30 year points on swap curve

Source: Credit Suisse

− Volatility skew and prepayment propensity: the MBS/swap yield spreads are

mainly attributed to the call options embedded in mortgages. The call option

valuation is driven by volatility assumptions and refinance propensity. This leads

to complex nonlinear behavior in mortgage rates loadings with regard to rates

change. For example, in a lognormal interest rate model, where rates volatilities

increase with rates, one would expect mortgage/swap spread (which is

proportional to option cost) to increase with rates if OAS stays constant for the

current coupon bond. As a result, mortgage rates would increase more than one-

to-one with regard to swap rates, i.e. the mortgage/swap beta, produced from the

IMS method, may be bigger than one in a lognormal model. As we discussed in a

previous report published on 20 September 2012 (Modeling and Analytics:

Neither normal, nor lognormal when it comes to volatility skew), volatility skew

changes with rates level. Hence, mortgage/swap beta should also change with

rates level.

Prepayment model choices also affect the profile of the IMS loadings. Many

models use present-value-saved as driver to define the refinance S-curve. Due to

the effect of discounting, this means a 3.5% mortgage with 50bps Refi incentive

has more refinance propensity than a 5.5% mortgage with the same 50bps Refi

incentive. If volatility assumptions are the same, the option cost and current

coupon/swap spread will be higher for a 3.5% current coupon mortgage than a

5.5% current coupon mortgage. This would suggest a less-than-one and

decreasing mortgage/swap beta, based on the IMS method. On the other hand,

as we discussed in the previous section, the volatility skew increases as rates

rally, which tends to increase the mortgage/swap beta. Combined, this leads to

complex behavior for mortgage/swap beta as a function of rates level.

0

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Flat Curve Steep Cuvre

Page 8: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 8

Credit Suisse mortgage rates model

As discussed previously, the mortgage rates model in the OAS model framework is a self-

reference mathematical problem. The IMS loadings (the mortgage rate sensitivities to

curve shocks) are based on the OAS model valuation, which has a mortgage rate model

embedded in itself. The embedded mortgage rate model produce its own mortgage rate

sensitivities to curve shocks. These two sets of mortgage rate sensitivities are often far

from being consistent.

Based on this intuition, the Credit Suisse mortgage rates model solves for a particular set of

model parameters that allows these two sets of loadings/mortgage rate sensitivities to be

consistent with each other. (The mathematical representations for this method are listed in

the appendix.) While the methodology is based on whole curve/IMS approach, the forward

projections of mortgage rates use a nonlinear combination of only 2/5/10 yr swap rates,

hence we have termed the Credit Suisse mortgage rate model as a “hybrid” in previous

sections. Using only 2/5/10 year rates to project mortgage rates in the stochastic simulation

does not reduce valuation accuracy compared with using the entire curve, because yield

curves in the stochastic simulations are usually “well behaved”/smooth and can be well

represented by just 2/5/10 year points. The partial duration shocks, on the other hand, can

be arbitrary, so we apply the IMS methodology. This “hybrid” combination allows the right

balance between computation efficiency and valuation accuracy, in our view.

While the Credit Suisse mortgage rate model/IMS method is constructed from the OAS

valuation approach, we can test its ability to forecast mortgage rates as well. For example,

we use the previous day/period’s OAS/spread and current day/period’s yield curve to

forecast the current day’s mortgage rate. We show that forecasting error from our method

is much smaller than that of a linear regression between mortgage rates and yield curve

points. (Exhibit 41 on page 39 of the Credit Suisse Agency Model Overview dated August

2010). This is remarkable, in our view, since the linear regression is an in-sample fit that

aims to minimize the “forecasting” error, while our IMS approach is valuation based and

does not use historical current coupon yield data directly, but it produces a much smaller

forecasting error. This provides some validation to the IMS methodology and Credit Suisse

mortgage rate model.

Page 9: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 9

Measure MBS curve risk under the IMS methodology

Exhibit 6: Yield curve risk measures are generally unbiased in CS models: low correlations between curve changes and model OAS changes for FNCL 3.5s

(Left panel) 1st and 2

nd Principal Components (PCA) for swap yields between Nov. 2010 and Nov. 2014; (Right panel)

Regression analysis between PCAs and FNCL 3.5s OAS

Source: Credit Suisse

While the Credit Suisse IMS methodology provides a consistent framework to measure yield

curve risk across MBS products and yield maturities, market prices are often affected by

factors outside of the OAS model framework. Exhibit 6 is an example of empirical analysis

separating these risk factors.

The left panel shows the 1st and 2

nd principal components (PCA) of swap curve daily

movement between the Novembers of 2010 and 2014. Pre-2009, PCA1 tends to mimic a

parallel curve shift. In recent years, however, the front end volatilities have been greatly

reduced, as a result, the 2yr and 5yr levels are only about 27% and 82% of the 10yr level in

the PCA1. The swaption implied volatility surfaces have a similar shape as well. The PCA2

represents a yield curve twist. The PCA1/PCA2 account for 89% and 9% of total variance of

yield curve variability during this period.

The right panel shows the correlation between FNCL 3.5s OAS and the PCA1/PCA2. If

model OAS are not correlated with yield curve movement, then model price changes, under

the constant OAS assumption, driven by changes in yield curve and volatility inputs, are

unbiased estimators of market price changes. Hence, model hedge ratios are effective if

correlations are low between OAS and yield curve changes. (The typical OAS model also

has a price change attribution component from current coupon yield. This is typically small in

our model. While we model the secular trend of MBS/swap basis, for example, QE related

mortgage basis changes, our view is that the MBS/swap basis is heavily traded and mean-

reverting, so we discount the high frequency part of the basis volatility. This leads to weaker

current coupon durations compared with a typical OAS model that carries forward the pricing

day’s MBS/swap basis forever. See the 11 December 2012 Modeling and Analytics: New

CS6.7 Model Release for detail. The appendix has some discussions on whether this

approach is consistent with non-arbitrage pricing framework.)

Exhibit 6 shows, for FNCL 3.5s, PCA2 is uncorrelated with OAS, while PCA1 has some

weak correlation, with regression R-square at 9.9% and a regression beta at 8.7. “Beta = 8.7”

means that for 1 unit of PCA1 curve movement (about 60bps at the 10yr point), OAS moves

8.7bps in the same direction. This implies that over this four year period of 2010-2014 the

empirical durations, on average, are slightly longer than model durations. And based on the

slopped shape of PCA1, most of the longer durations are attributed to the backend of the

yield curve (the empirical partial durations are longer in the backend of the yield curve).

-80

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s

Term (yr)

PCA1 PCA2

y = 8.7246xR² = 0.0994

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AS

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Change of PCA1

y = -5.4125xR² = 0.0038

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Page 10: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 10

Exhibit 7 shows similar performance patterns across 30yr and 15yr coupon stacks. The R-

square and beta for the 15yr stacks are much smaller than the 30yr, implying more

effective model hedge ratio performance in the 15yr sector.

Exhibit 7: Weak correlations and positive beta between OAS and PCA1 imply on average slightly longer durations for the coupon stack vs. model durations

OAS correlation with PCA1 and PCA2 across 30yr and 15yr coupon stack; Nov. 2010 – Nov. 2014; the regression beta is in the unit of bps OAS per PCA1/PCA2 movement

PCA1 vs. OAS PCA2 vs. OAS

Regression R-square Regression beta Regression R-square Regression beta

FNCL 3s 0.10 9.7 0.02 -12.5

FNCL 3.5s 0.10 8.7 0.00 -5.4

FNCL 4s 0.07 7.3 0.00 3.3

FNCL 4.5s 0.05 6.3 0.01 8.6

FNCI 3s 0.03 4.7 0.00 0.39

FNCI 3.5s 0.01 2.1 0.01 9.5

Source: Credit Suisse

However, this “average” view over 4 years might be misleading, as model bias could be

concentrated in certain historical periods and in certain price ranges. We apply the same

analysis to the 60 days rolling regression between model OAS and PCA1 to exam the

model hedge ratio performance patterns across the period of 2011-2014. Since low R-

square values may indicate spurious correlation where beta values have little significance,

we use the regression beta “weighted” by R-square values as indicator.

Exhibit 8: Three periods of model hedge ratio “failures”: QE related high OAS directionalities in Aug-Sep 2011 and July-Aug 2013, and high model risk (high premium and prepayment volatility) around July 2012

60 days rolling regression between OAS and PCA1, Product of regression beta and R-square for FNCL 3.5s and 4s for 2011-2014 (unit: bps/PCA1)

Source: Credit Suisse

-5

0

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-10123456789

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Ma

r-1

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3.5s (left-axis) 4s (right-axis)

Page 11: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 11

Exhibit 8 shows the value of this indicator for FNCL 3.5s and 4s across 2011-2014. Three

periods of model hedge ratio “failures” (with regard to predicting market price changes)

stand out, while model hedge ratios are generally realistic curve risk measures outside of

these three periods.

− The periods of Aug-Sep 2011 and July-Aug 2013 saw high volatilities in both rates

and MBS basis due to market perceptions of the Federal Reserve’s QE asset

purchase programs. Both treasuries and MBS were affected in similar fashion in the

asset purchase programs, which led to high positive correlations between rates and

MBS basis. Exhibit 8 shows this pattern mostly affected 3.5s (the then production

coupon which was the main target of Fed purchases), and less for the 4s.

− July 2012 saw rates reaching historical lows, and 3.5s and 4s were at $106-107

high premium territories. Prepayment performances were highly volatile over this

period. Furthermore, there is little historical data for prepayment analysis to rely

on when the MBS universe reached this high premium level, and model risk is

high given uncertainties about borrowers’ and servicers’ behaviors. Credit

Suisse's model appeared to significantly under-hedge market price movements

for 3.5s and 4s during this period. One possible driver for this discrepancy could

be our model’s forward mortgage credit availability assumption. The model

assumes mortgage underwriting recovery in 5 years (average prepayment

propensity increases by 60% from then current levels, when the “macro credit

variable” increases from 0.5 to 0.8) (see pages 3-4 of the 21 January 2014

Modeling and Analytics: New agency model CS6.9 released to Locus.) This might

be biased to the optimistic side versus the market view, hence model durations

might be too short for high premium coupons.

Exhibit 9 shows similar behavior for 15yr TBA stack. Note FNCI 3.5s had both positive and

negative directionality periods during the high premium period of July 2012 to Feb. 2013.

Exhibit 9: Similar performance patterns for the 15yr sector

60 days rolling regression between OAS and PCA1, Product of regression beta and R-square for FNCI 3s and 3.5s for 2011-2014 (unit: bps/PCA1)

Source: Credit Suisse

Understanding the sources of model discrepancy from market price performance is

important if we need to extend model adjustments to other MBS products that do not have

liquid price information, and thus cannot afford this kind of empirical analysis. In this

context, we discuss a common market practice of comparing model durations to “trader

durations” as part of model validation process.

-6

-4

-2

0

2

4

6

8

10

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-11

Ma

r-1

1

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p-1

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1

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-12

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Se

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2

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2

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13

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3

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3

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p-1

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Nov-1

4

3s 3.5s

Page 12: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 12

Exhibit 10: FNCL 4s: compare "trader durations", model durations and an ex-post duration target: model durations seem to be biased longer?

The ex-post duration target regresses between TBA prices and 10yr swap rates for future 20 days. The “goodness” of “trader durations” and model durations are measured by their distances to this duration target

Source: Credit Suisse

TBA “trader duration” is a form of market view of future hedge ratios between TBA and 10

year swap/treasuries. Exhibit 10 shows the comparison between “trader durations”, model

durations and an ex-post duration target for FNCL 4s. The ex-post duration target

regresses between TBA prices and 10yr swap rates for future 20 days, hence this is the

“best” hedge ratio/duration measure if one has perfect information for the future. Hence,

the “goodness” of either “trader durations” or model durations is measured by their

distances to this ex-post duration target.

Overall, the “trader durations” track the ex-post duration target well, revealing the high

skills of the market in anticipating price actions. Model durations, on the other hand, tend

to be generally longer than “trader durations” and the ex-post duration measures, except

around July-August 2012. Does this mean that the model is doing well for July-August

2012, and may need to be adjusted for the rest of the time periods?

Exhibit 11:FNCL 4s: model durations, once adjusted for the shape of PCA1, track the ex-post duration target well

The ex-post duration target regresses between TBA prices and 10yr swap rates for future 20 days. The “goodness” of “trader durations” and model durations is measured by their distances to this duration target

Source: Credit Suisse

0

1

2

3

4

5

6

7

8

Jan

-11

Ma

r-1

1

Ma

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1

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11

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No

v-1

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Jan

-12

Ma

r-1

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2

No

v-1

2

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13

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3

No

v-1

3

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p-1

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Target Dur. Trader's Dur Model Dur.

0

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7

8

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No

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Jan

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Ma

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No

v-1

2

Jan

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Ma

r-1

3

Ma

y-1

3

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13

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No

v-1

3

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Ma

y-1

4

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p-1

4

Target Dur. Trader's Dur Model Dur.with PCA1 Adj.

Page 13: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 13

On the contrary, we would argue quite the opposite, that the model provides good hedge

ratios for market prices for much of the periods, except July-August 2012, and July-August

2013. Note that model durations are computed with the assumption of parallel yield curve

shift, while, as discussed previously, yield curve movements in recent years are

distinctively slopped with much diminished volatilities for the front end. Hence, once

adjusted for the shape of PCA1, the model duration measure tracks well the “trader

durations” and the ex-post duration target, except for July-August 2012 and July-August

2013 when OAS directionality was very strong, as discussed in previous sections. Note

that, for recent periods, the PCA1 adjusted durations for 4s are about 1yr shorter than

standard model durations, and this measure generally outperformed the “trader durations”

for much of 2014.

Exhibit 12:FNCL 4s: adjust the model durations further with ex-post OAS directionality

The ex-post duration target regresses between TBA prices and 10yr swap rates for future 20 days. The “goodness” of “trader durations” and model durations is measured by their distances to this duration target

Source: Credit Suisse

If we adjust the PCA1 model durations further, with an ex-post correlation between 4s

OAS and 10yr swap rates for future 20 days (applying the differentiation chain rule by

combining yield curve duration and OAS spread duration), the resulting model durations

track the ex-post duration target well.

Obviously, it might be difficult to forecast the future correlations between OAS and yield

curve. Given the information content of the “trader durations”, one can back out the implied

future correlations between OAS and yield curve from the differences between the “trader

durations” and the PCA1 adjusted model durations, and apply this information consistently

across maturities and other related MBS products.

0

2

4

6

8

Jan

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Ma

r-1

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Ma

y-1

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p-1

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No

v-1

1

Jan

-12

Ma

r-1

2

Ma

y-1

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12

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v-1

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r-1

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3

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p-1

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Target Dur.

Trader's Dur

Model Dur. with PCA1&OAS directionality Adj.

Page 14: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 14

Exhibit 13: FNCI 3.5s: PCA1 adjusted model duration generally outperforms “trader durations” except in the period of Nov. 2012-March 2013 due to high and negative OAS directionality

The ex-post duration target regresses between TBA prices and 10yr swap rates for future 20 days. The “goodness” of “trader durations” and model durations is measured by their distances to this duration target

Source: Credit Suisse

Exhibit 13 shows similar performance patterns for 15yr 3.5s. Note that the PCA1 adjusted

model duration generally outperforms “trader durations” except in the period between

November 2012 to March 2013 due to high and negative OAS directionality. For recent

periods, the PCA1 adjusted durations are about 1yr shorter than the standard (parallel)

durations.

In summary, we believe the IMS methodology provides a consistent framework to model

MBS curve risk across yield maturities and MBS products, and an additional overlay of

empirical analysis is needed for periods of high market price volatilities due to

supply/demand shocks and high model risk issues.

0

1

2

3

4

5

6

Jan

-11

Ma

r-1

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y-1

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p-1

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No

v-1

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Jan

-12

Ma

r-1

2

Ma

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No

v-1

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Ma

r-1

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No

v-1

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Ma

r-1

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y-1

4

Jul-

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p-1

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Target Dur. Trader Dur Model Dur.with PCA1 Adj.

Page 15: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 15

Appendix: Formulations for IMS methodology and Credit Suisse mortgage rates model; additional discussions Formulations for IMS partials We list two methods of implementing the IMS methodology here

4

1) Recognize the current coupon yield is often computed by interpolating the coupons of the two TBA prices bracketing par

( ) ( )

P are the prices of the two TBA prices. Based on OAS pricing model:

( )

Apply differentiation and chain rules:

Apply substitution to obtain IMS loadings (sensitivities of mortgage rates to swap curve

shocks)

(

)

(

)

2) Follow the insight that current coupon mortgage rate is the yield of a par pass-

through bond

( ) Where

Apply differentiation to swap curve shocks

4 The formulation is for illustration purpose. Implementation needs to take into account of TBA settlement convention as well as

the existing mortgage rates sensitivities to interest rate curve in the model.

Page 16: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 16

Solving for IMS loadings (sensitivities of mortgage rates to swap curve shocks)

Using either method to obtain the IMS loadings

, then MBS partial durations can be

consistently computed across all product types and across all maturities and shock types.

Formulations for Credit Suisse mortgage rate model

Follow the insight that current coupon mortgage rate is the yield of a par pass-through

bond. Use 2/5/0 year swap to represent the swap curve. Also note that the OAS model

includes the mortgage rate/current coupon model.

( )

Follow the same derivation of the IMS loadings, and require these loadings to be

consistent with the mortgage rate sensitivities from the current coupon model

This is a fixed point problem for functions.5 One can parameterize the functions based on

insight of the nonlinear mortgage rate properties discussed in previous sections. Solving

for these parameters typically requires only 2-3 iterations.

Validity of IMS methodology and assumptions

The dearth of traded TBA prices across future settlement dates makes it a little difficult to

model mortgage rates in the non-arbitrage framework. The IMS methodology assumes

that OAS of current coupon bonds are uncorrelated with yield curves. As discussed in

previous sections, empirical data generally support this assumption.

Note that the typical “OAS directionality” issue does not contradict this assumption. “OAS

directionality” refers to the observation that OAS of a predetermined TBA/pass-through

security tends to widen with a rates rally. In the IMS methodology, the “cc bonds” changes

with the yield curve.

In addition, the trend of “cc bond” OAS or MBS/swap basis can be modeled in the same

framework by adding a time dependent component to the “constant OAS” mortgage rates

process. Many OAS models assume the pricing day’s MBS/swap basis/spread stay

5 For example, "On the existence of the endogenous mortgage rate process", Yevgeny Goncharov, Mathematical Finance, Volume

22, Issue 3, pp. 475-487, July 2012

Page 17: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 17

perpetually, which leads to significant current coupon durations for MBS. Our view is that

the MBS/swap basis is heavily traded, so we discount the high frequency part of the basis

volatility with strong mean reversion. This leads to weaker current coupon durations. At the

same time, we do model the trend of MBS basis, for example, the recent mortgage basis

tightening and widening caused by various QE related issues. The combination of

modeling the basis trend and suppressing the high frequency part of the basis volatility is

validated by the empirical behavior of MBS/swap basis going through the various QE

programs.

The IMS methodology can be further expanded by adding additional factors of MBS/swap

basis that are correlated with swap curves. This can potentially help model the OAS

directionality issue discussed in previous sections.

One valid criticism is the inconsistency of the price attribution process using the IMS partials. Follow the formulations from the previous section on the mortgage rate model, the regular

partial durations are computed with the mortgage rates sensitivities

from the

embedded mortgage rates model, while the IMS partial durations use, instead, the valuation

implied sensitivities

. Since the OAS are computed using the former set of sensitivities

, using IMS partials for the price change attribution process seems to be inconsistent.

(In the case of 2/5/10 year partial durations in Credit Suisse's model, the two sets of sensitivities are consistent as discussed in previous sections, thus this issue is muted.)

It is useful to note that the OAS model itself is fundamentally inconsistent, when these two

sets of sensitivities are inconsistent. If using a computationally expensive “whole curve

constant OAS” mortgage rate model is the ultimate “consistent” model, then the main

deficiency of using a simple mortgage rate model (for example, a 10yr rate based mortgage

rate model) may be the resulting questionable partial duration profile, while the OAS

valuation is reasonably close. 6 Overlaying IMS partial durations would correct much of the

partial duration profile, and improve the curve risk measure across maturities and MBS

products at a modest computational cost. The effectiveness of the IMS correction of the

partial duration profile (even when the underlying mortgage rate model is overly simplistic) is

due to the quick convergence property of using iterations in this self-reference problem.

In reality, the price change attribution “leakage” (price changes that cannot be attributed to

market variables such as yield curve and volatility changes ) due to using the IMS partials

is generally small, and is of similar magnitude as other “leakages” caused by other types

of modeling imperfections, for example:

− Weekly primary mortgage rates update: while our primary/secondary mortgage

rate spread model aims to forecast the primary rates both for short term and long

term, it inevitably has errors when the primary rates are “marked-to-data” weekly,

thus creating price attribution leakage.

− Monthly HPI update and quarterly forecast update: while our HPA models aim to

forecast national/state/MSA level HPA/HPIs, model forecasting errors and our

quarterly updating forecasts process will create price attribution leakage.

− Monthly factor update: prepayment and default model forecasts are never perfect,

hence monthly pool factor updates also generate price attribution leakage.

− Monthly loan/pool level attributes change: the model uses loan/pool attributes (for

example, loan size, WAC, FICO, etc.) to project prepayment and default. And, to

some extent, the model also tries to project drifts of these attributes over time due

to loan level inhomogeneity in the pools/securities. The inconsistences between

projected attributes drifts and actual attributes changes lead to price attribution

leakage.

6 For example, see discussion on pages 168-173 Davidson & Levin, "Mortgage Valuation Models" Oxford University Press 2014

Page 18: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

01 December 2014

Modeling and Analytics 18

Similar to models in each example (primary/secondary spread model, HPA models, etc.),

the IMS methodology, while subject to small price attribution leakage, serves a useful

purpose of improving valuation and hedging.

The analysis of OAS directionality is shown as a residual curve risk after applying IMS

methodology. This analysis provides insight to the development of a “Market Implied

Model” (or so-called prepayment model risk adjusted model). We identified two types of

OAS directionality, the supply/demand driven (for example, the QE induced high OAS

directionality for par coupons) versus model risk driven for premium coupons. Different

“implied model tuning” approaches might be needed to model these two types of issues.

Page 19: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

GLOBAL FIXED INCOME AND ECONOMICS RESEARCH

Ric Deverell

Global Head of Fixed Income and Economics Research

+1 212 538 8964

[email protected]

GLOBAL SECURITIZED PRODUCTS RESEARCH

Roger Lehman

Global Head of Securitized Products Research

+1 212 325 2123

[email protected]

RESIDENTIAL MORTGAGES CMBS

Mahesh Swaminathan Roger Lehman, Managing Director

Group Head Group Head

+1 212 325 8789 +1 212 325 2123

[email protected] [email protected]

AGENCY MBS NON-AGENCY MBS

Qumber Hassan Marc Firestein Serif Ustun, CFA Sylvain Jousseaume, CFA

+1 212 538 4988 +1 212 325 4379 +1 212 538 4582 +1 212 325 1356

[email protected] [email protected] [email protected] [email protected]

Glenn Russo Jonathan Corwin

+1 212 538 6881 +1 212 538 6490

[email protected] [email protected]

EUROPE JAPAN

Helen Haworth, CFA Tomohiro Miyasaka

Group Head +81 3 4550 7171

+44 20 7888 0757 [email protected]

[email protected]

Carlos Diaz Marion Pelata

+44 20 7888 2414 +44 20 7883 1333

[email protected] [email protected]

MODELING AND ANALYTICS

David Zhang

Group Head

+1 212 325 2783

[email protected]

Yihai Yu

+1 212 325 7922

[email protected]

Taek Choi

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Oleg Koriachkin

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Joy Zhang

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Page 20: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

Disclosure Appendix

Analyst Certification David Zhang, Joy Zhang and Yihai Yu each certify, with respect to the companies or securities that the individual analyzes, that (1) the views expressed in this report accurately reflect his or her personal views about all of the subject companies and securities and (2) no part of his or her compensation was, is or will be directly or indirectly related to the specific recommendations or views expressed in this report.

Important Disclosures Credit Suisse's policy is only to publish investment research that is impartial, independent, clear, fair and not misleading. For more detail, please refer to Credit Suisse's Policies for Managing Conflicts of Interest in connection with Investment Research: http://www.csfb.com/research-and-analytics/disclaimer/managing_conflicts_disclaimer.html . Credit Suisse's policy is to publish research reports as it deems appropriate, based on developments with the subject issuer, the sector or the market that may have a material impact on the research views or opinions stated herein. The analyst(s) involved in the preparation of this research report received compensation that is based upon various factors, including Credit Suisse's total revenues, a portion of which are generated by Credit Suisse's Investment Banking and Fixed Income Divisions. Credit Suisse may trade as principal in the securities or derivatives of the issuers that are the subject of this report. At any point in time, Credit Suisse is likely to have significant holdings in the securities mentioned in this report. As at the date of this report, Credit Suisse acts as a market maker or liquidity provider in the debt securities of the subject issuer(s) mentioned in this report. For important disclosure information on securities recommended in this report, please visit the website at https://firesearchdisclosure.credit-suisse.com or call +1-212-538-7625. For the history of any relative value trade ideas suggested by the Fixed Income research department as well as fundamental recommendations provided by the Emerging Markets Sovereign Strategy Group over the previous 12 months, please view the document at http://research-and-analytics.csfb.com/docpopup.asp?ctbdocid=330703_1_en . Credit Suisse clients with access to the Locus website may refer to http://www.credit-suisse.com/locus For the history of recommendations provided by Technical Analysis, please visit the website at www.credit-suisse.com/techanalysis . Credit Suisse does not provide any tax advice. Any statement herein regarding any US federal tax is not intended or written to be used, and cannot be used, by any taxpayer for the purposes of avoiding any penalties.

Emerging Markets Bond Recommendation Definitions Buy: Indicates a recommended buy on our expectation that the issue will deliver a return higher than the risk-free rate. Sell: Indicates a recommended sell on our expectation that the issue will deliver a return lower than the risk-free rate.

Corporate Bond Fundamental Recommendation Definitions Buy: Indicates a recommended buy on our expectation that the issue will be a top performer in its sector. Outperform: Indicates an above-average total return performer within its sector. Bonds in this category have stable or improving credit profiles and are undervalued, or they may be weaker credits that, we believe, are cheap relative to the sector and are expected to outperform on a total-return basis. These bonds may possess price risk in a volatile environment. Market Perform: Indicates a bond that is expected to return average performance in its sector. Underperform: Indicates a below-average total-return performer within its sector. Bonds in this category have weak or worsening credit trends, or they may be stable credits that, we believe, are overvalued or rich relative to the sector. Sell: Indicates a recommended sell on the expectation that the issue will be among the poor performers in its sector. Restricted: In certain circumstances, Credit Suisse policy and/or applicable law and regulations preclude certain types of communications, including an investment recommendation, during the course of Credit Suisse's engagement in an investment banking transaction and in certain other circumstances. Not Rated: Credit Suisse Global Credit Research or Global Leveraged Finance Research covers the issuer but currently does not offer an investment view on the subject issue. Not Covered: Neither Credit Suisse Global Credit Research nor Global Leveraged Finance Research covers the issuer or offers an investment view on the issuer or any securities related to it. Any communication from Research on securities or companies that Credit Suisse does not cover is a reasonable, non-material deduction based on an analysis of publicly available information.

Corporate Bond Risk Category Definitions In addition to the recommendation, each issue may have a risk category indicating that it is an appropriate holding for an "average" high yield investor, designated as Market, or that it has a higher or lower risk profile, designated as Speculative, and Conservative, respectively.

Credit Suisse Credit Rating Definitions Credit Suisse may assign rating opinions to investment-grade and crossover issuers. Ratings are based on our assessment of a company's creditworthiness and are not recommendations to buy or sell a security. The ratings scale (AAA, AA, A, BBB, BB, B) is dependent on our assessment of an issuer's ability to meet its financial commitments in a timely manner. Within each category, creditworthiness is further detailed with a scale of High, Mid, or Low − with High being the strongest sub-category rating: High AAA, Mid AAA, Low AAA - obligor's capacity to meet its financial commitments is extremely strong; High AA, Mid AA, Low AA − obligor's capacity to meet its financial commitments is very strong; High A, Mid A, Low A − obligor's capacity to meet its financial commitments is strong; High BBB, Mid BBB, Low BBB − obligor's capacity to meet its financial commitments is adequate, but adverse economic/operating/financial circumstances are more likely to lead to a weakened capacity to meet its obligations; High BB, Mid BB, Low BB − obligations have speculative characteristics and are subject to substantial credit risk; High B, Mid B, Low B − obligor's capacity to meet its financial commitments is very weak and highly vulnerable to adverse economic, operating, and financial circumstances; High CCC, Mid CCC, Low CCC – obligor's capacity to meet its financial commitments is extremely weak and is dependent on favorable economic, operating, and financial circumstances. Credit Suisse's rating opinions do not necessarily correlate with those of the rating agencies.

Page 21: Fixed Income Research FOR INSTITUTIONAL CLIENT USE ONLY

Credit Suisse’s Distribution of Global Credit Research Recommendations* (and Banking Clients)

Global Recommendation Distribution** Buy <1% (<1% banking clients) Outperform <1% (<1% banking clients) Market Perform 100% (100% banking clients) Underperform <1% (<1% banking clients) Sell <1% (<1% banking clients) *Data are as at the end of the previous calendar quarter. **Percentages do not include securities on the firm’s Restricted List and might not total 100% as a result of rounding.

Backtested, Hypothetical or Simulated Performance Results Backtested, hypothetical or simulated performance results have inherent limitations, some of which are described below. Unlike an actual performance record based on trading actual client portfolios, backtested, hypothetical or simulated results are achieved by means of the retroactive application of a backtested model itself designed with the benefit of hindsight. Backtested performance does not reflect the impact that material economic or market factors might have on an adviser's decision-making process if the adviser were actually managing a client’s portfolio. The backtesting of performance differs from actual account performance because the investment strategy may be adjusted at any time, for any reason, and can continue to be changed until desired or better performance results are achieved. The backtested performance includes hypothetical results that do not reflect the reinvestment of dividends and other earnings or the deduction of advisory fees, brokerage or other commissions, and any other expenses that a client would have paid or actually paid. No representation is made that any account will or is likely to achieve profits or losses similar to those shown. Alternative modeling techniques or assumptions might produce significantly different results and prove to be more appropriate. Past hypothetical backtest results are neither an indicator nor guarantee of future returns. In fact, there are frequently sharp differences between hypothetical performance results and the actual results subsequently achieved. Actual results will vary, perhaps materially, from the analysis. In addition, hypothetical trading does not involve financial risk, and no hypothetical trading record can completely account for the impact of financial risk in actual trading. For example, the ability to withstand losses or to adhere to a particular trading program in spite of trading losses are material points which can also adversely affect actual trading results. There are numerous other factors related to the markets in general or to the implementation of any specific trading program which cannot be fully accounted for in the preparation of hypothetical performance results and all of which can adversely affect actual trading results. As a sophisticated investor, you accept and agree to use such information only for the purpose of discussing with Credit Suisse your preliminary interest in investing in the strategy described herein.

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The investments and services contained or referred to in this report may not be suitable for you and it is recommended that you consult an independent investment advisor if you are in doubt about such investments or investment services. Nothing in this report constitutes investment, legal, accounting or tax advice, or a representation that any investment or strategy is suitable or appropriate to your individual circumstances, or otherwise constitutes a personal recommendation to you. CS does not advise on the tax consequences of investments and you are advised to contact an independent tax adviser. Please note in particular that the bases and levels of taxation may change. Information and opinions presented in this report have been obtained or derived from sources believed by CS to be reliable, but CS makes no representation as to their accuracy or completeness. 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Investment principal on bonds can be eroded depending on sale price or market price. In addition, there are bonds on which investment principal can be eroded due to changes in redemption amounts. Care is required when investing in such instruments. When you purchase non-listed Japanese fixed income securities (Japanese government bonds, Japanese municipal bonds, Japanese government guaranteed bonds, Japanese corporate bonds) from CS as a seller, you will be requested to pay the purchase price only.