Download presentation

Presentation is loading. Please wait.

Published byPaulina Coleman Modified over 4 years ago

1
Suspecting the Rating Agencies Dan diBartolomeo Northfield Information Services January 2012

2
The Matter At Hand One of the largest contributing factors to the Global Financial Crisis of 2008-2009 was the huge number of fixed income instruments with very high ratings (e.g. AAA) that were either severely downgraded or went into actual default. All three of the major rating agencies, Moodys, Standard and Poors, and Fitch were shown to be seriously deficient in their ratings of a variety of debt instruments, particularly complex instruments (e.g. Credit Default Obligations or CDOs). The rating agencies failed again with the obligations of major financial institutions such demonstrated by the spectacular collapses of firms such as AIG, Bear Stearns and Lehman Brothers.

3
Some Unpleasant Outcomes From the first quarter 2005 through the third quarter of 2007, two thirds of CDOs S&P had rated were downgraded. From the first quarter 2005 through the third quarter of 2007, two thirds of CDOs S&P had rated were downgraded. 44% of all CDOs were downgraded to speculative or in default 44% of all CDOs were downgraded to speculative or in default Over the same time, 17% of sub-prime residential mortgage securities were downgraded Over the same time, 17% of sub-prime residential mortgage securities were downgraded 9.8% were downgraded to speculative or in default 9.8% were downgraded to speculative or in default $250 Billion in major bank write offs from January 1, 2007 through April 2008, another $1.3 Trillion estimated from April 2008 to date $250 Billion in major bank write offs from January 1, 2007 through April 2008, another $1.3 Trillion estimated from April 2008 to date

4
When Money Is At Stake, Cheat! S&P has admitted to notching ratings on many securitized instruments S&P has admitted to notching ratings on many securitized instruments If an issuer wanted a rating done in a hurry, S&P would simply assume a rating of one grade lower than whatever S&P or Moodys had most recently rated the debt of the same issuer If an issuer wanted a rating done in a hurry, S&P would simply assume a rating of one grade lower than whatever S&P or Moodys had most recently rated the debt of the same issuer To my mind, this is fraud To my mind, this is fraud The expectations of financial market participants is that rating agencies actually conduct some form of credit analysis before issuing a rating The expectations of financial market participants is that rating agencies actually conduct some form of credit analysis before issuing a rating At a cocktail party, a securitization lawyer for S&P rebuked me, saying they had done nothing illegal, as there are no actual requirements for any analysis At a cocktail party, a securitization lawyer for S&P rebuked me, saying they had done nothing illegal, as there are no actual requirements for any analysis

5
Beating the Agencies at their Own Game At previous QWAFAFEW events we have described an approach to combine equity factor risk models and structural models of credit risk to provide consistent measures of equity risk, default risk and default correlation. The most important metric arising from this process is a market implied expected life of a firm. We employ this as a quantitative measure of the sustainability of firms In this presentation we will show how the a simple model using the expected life metric captured bankruptcy risk during the Global Financial Crisis and was predictive of subsequent credit rating changes and defaults We will also show that a related simple portfolio strategy would resulted in significant alpha for US fixed income portfolios during the most stressful portion of the GFC

6
Basic Contingent Claims Literature Merton (1974) poses the equity of a firm as a European call option on the firms assets, with a strike price equal to the face value of the firms debt Alternatively, lenders are short a put on the firm assets Default can occur only at debt maturity Black and Cox (1976) provide a first passage model Default can occur before debt maturity Firm extinction is assumed if asset values hit a boundary value (i.e. specified by bond covenants) Leland (1994) and Leland and Toft (1996) Account for the tax deductibility of interest payments and costs of bankruptcy Estimate boundary value as where equity value is maximized subject to bankruptcy

7
Reverse the Concept: Sustainability Instead of trying to estimate how likely it is that firm goes bankrupt, lets reverse the logic We will estimate the market implied expected life of firms using contingent claims analysis Formally, our measure is the median of the expectation of the distribution of the life of the firm Makes different default probabilities for different bond issues very natural as each maturity will lie at a different point in the survival time distribution Firms with no debt can now be included since it is possible that they get some debt in the future and default on that A quantitative measure of the fundamental and social concept of sustainability

8
Our Basic Option Pricing Exercise Underlying is the firms assets with asset volatility determined from the equity factor model How volatile would a firms stock be if the firm had no debt? This is the volatility of the assets Solve numerically for the implied expiration date of the option that equates the option values to the stock price Market implied expected life of the firm See Yaksick (1998) for numerical methods for evaluating a perpetual American option Include a term structure of interest rates so that as the implied expiration date moves around, the interest rate changes appropriately

9
Our Previously Published Research diBartolomeo, Journal of Investing, December 2010 Used equity volatilities from Northfield US Fundamental Model One year horizon for risk forecast Near horizon model are more suitable but less history available Estimate monthly for all firms in Northfield US equity universe from December 31, 1991 to March 31, 2010 Study three samples: All Financial firms Non-financial firms Sources of Time series variation Stock prices, debt levels, Northfield risk forecasts Mix of large and small firms, 4660 <= N <= 8309

10
A Digression on Too Big to Fail For the full sample period of 1992 through March 31, 2010 Non Financials: Median 14.74, Cap Weighted 18.42 Revenue Weight 17.60 Financials: Median 22.28, Cap Weighted 17.06 Revenue Weighted, 7.86 Too Big to Fail is really real Risk taking is heavily concentrated in the largest financial firms Risk taking has been concentrated in the largest financial firms for at least 20 years

11
Quantifying Sustainability MSCI KLD DSI 400 index of US large cap firms considered socially responsible, 20 year history Typically about 200 firms in common with the S&P 500 July 31, 1995 DSI 400, Median 17, Average 17.91, Standard Deviation 9.93 S&P 500, Median 14, Average 15.40, Standard Deviation 9.28 Difference in Means is statistically significant at 95% level March 31, 2010 DSI 400, Median 30, Average 26.39, Standard Deviation 11.45 S&P 500, Median 30, Average 24.93, Standard Deviation, 10.92 Difference in Means is statistically significant at 90% but not 95% Testing on Disjoint Sets (DSI NOT S&P, S&P NOT DSI) Statistically significant difference in means for every time period tested

12
Results to Sustainability Equity Investing (1992 through March 2010) Table 1 1 MeanAnnualLeveraged MonthlyCumulativeMonthlyCompoundS&P Risk Return Standard DeviationReturn Equivalent Return Q5 Equal1.33713.779.1510.907.45 Q1 Equal1.03790.863.6411.5012.83 Q5 Cap0.77251.606.624.984.76 Q1 Cap0.79414.323.787.778.26 S&P 500 2 0.75347.744.326.78

13
Combining Sustainability and MV (1992 through March 2010, 200 Max Positions) Mean Monthly CumulativeMonthly Standard Deviation Annual Compound Return Annual Sharpe Ratio Q1 MV 1.07840.432.9612.34.81 Q5 MV 1.772901.156.8019.33.71

14
We combined rating levels from S&P, Moodys and Fitch into a unified letter scheme Each rating level was assigned a numerical value A rating of AAA was 10 on the numeric scale A rating of D (default) was 1 on the scale Intermediate levels of AA,A,BBB,BB,B,CCC,CC,C A + added.333 A - subtracted.333 The scale is convenient but does not reflect any actual differences in probability of default (PD) or economic loss given default (LGD)

15
As part of our normal fixed income analysis we estimate option-adjusted spreads for about 6 Million fixed income instruments on a monthly basis Measures the portion of bond yield not associated with time value of money. This is premium for credit risk and illiquidity The median of the OAS values for set of the category members is used Monthly history available to 2001 Bonds are broken into about 800 categories based on rating, geographic region of issue and sector Computational model assumes lognormal interest rates and combines features from Fabozzi and Dattatreya (1989) and Black, Derman and Toy (1990). We can keep AAA ratings at 10, and D at 1 but rescale intermediate levels inversely proportional to OAS

16
RatingSimple NumericOAS Spread BPSpread Numeric AAA108610 AA9899.96 A81079.73 BBB71499.20 BB62877.47 B53646.50 CCC44285.69 CC34555.35 C24944.86 D18011

17
We wanted a really clean history of US bond rating changes across all rating agencies We sent a temp (a classmate of mine) to the Boston Public Library to hand collect every rating change published in Barrons from 1992 to 2008 Information was hand entered into spreadsheets and then matched to issuers, in a partly automated, partly manual way It took roughly four months of tough full time effort There are roughly 8500 events in the data set and we have been able match about 6500 of those to entities with publicly traded equity The good news is that Steve was so good that he is now a very valued member of our Boston tech support staff

18
Our summer intern was then left to do an event study type model of the rating changes for the subset of US corporate bonds The big job is merging the expected life data derived from equities to issue level bond data It sounds easy but it is really a mess to track the related equity across mergers, acquisitions and spin-offs All data was standardized to make pooling across time easier Dependent variable was the percentage change in the simple numerical value of the credit rating Independent variables: 12 month percentage change in expected life as of prior month end 12 month change in the cross-sectional Z-score of expected life within the US equity universe Ethan survived too

19
We converted all data to rank values within the pooled sample In-sample our model had a correlation of about 40% (R- squared =.16) A very high degree of statistical significance on coefficients (T > 4) R-squared was higher for subsets of lower grade bonds (i.e. NOT A) Even with our simple model we could meaningfully predict subsequent changes in bond ratings These results are all conditional that a change in rating would eventually take place since only such events existed in our data Non-events (no rating change) were excluded from the sample by design Perhaps our model would predict 14 of every 5 downgrades

20
Universe is all US corporate bonds in the Northfield Everything Everywhere model Typical size around 18,000 bond issues Study period from December 31, 2005 to June 30, 2011 Minimum maturity one year Each bond is matched to contemporaneous expected life of issuer Assignments are updated annually for mergers, acquisitions Return performance calculations exclude bonds with price outliers at the start of the period

21
It should be intuitive that bonds with higher ratings should be associated with issuers with longer expected lives Break all bonds into 20 rating categories (including + and -) Calculate average expected life for all bonds in each rating category Correlate the average expected life and our simple numeric rating At 12/31/2005, the correlation across categories was +.68 Sample size of 17445 issues At 12/31/2007 (pre bailouts), the correlation was -.35 Sample size of 22069 issues By 12/31/2008, (post bailouts) the correlation was +.27 Sample size of 20043 issues

22
At each year end starting at 2005 we convert the expected life of issuer for each bond issue to a Z score within rating category A negative Z score indicates that our metric suggests that the firm is less creditworthy than the published rating Sort universe of 22000 bond issues into quintiles by Z score At 12/31/2006: Of the bottom quintile of 4400 bond issues, 2940 were from Wall Street firms that either went bankrupt, were acquired or needed major government assistance The rogues gallery included: Bear Stearns (534 issues), Merrill Lynch (868), Lehman Brothers (657), Morgan Stanley (257), CIT Financial (338), Countrywide (136) and Washington Mutual (24) Nearly identical result for 12/31/2007

23
US government intentions to mount the TARP bailout were announced on October 3, 2008 with most of the details filled in a couple weeks later. At October 31, 2008, the cumulative Q1/Q5 return spread was more than 1200 basis points in less than three years on widely diverse portfolios (equal weight across issues). The cumulative return spread peaked in December 2008 and declined back to almost exactly zero by June 2011. The implicit and explicit guarantees by the US Treasury and Federal Reserve had essentially driven the perceived creditworthiness of corporate bonds back to pre- GFC levels

24
Other Agencies: The Lace Case Lace Financial is a small US rating agency specializing in community banks, credit unions and insurance companies Santoni and Arbia (2010) studied the effectiveness of the Lace ratings on small US banks 116 small banks rated by Lace went under in 2009 72% of the failed banks were rated E (lowest non-investment grade) at least a year before actual failure 94% of the failed banks were rated E six months before the actual failure Clearly, the Lace ratings were effective but maybe its just an issue of answering an easy question. Analyzing a small community bank may just be that much easier than a complex, global entity like Citigroup or Lehman Brothers.

25
Lets Start at the Beginning In the late 1990s, Moodys began to provide credit ratings of securitized corporate loans (CLO) based on a method known as the Binomial Expansion Technique In the late 1990s, Moodys began to provide credit ratings of securitized corporate loans (CLO) based on a method known as the Binomial Expansion Technique Once a default probability had been estimated for loans in a pool, the probabilities of potential multiple defaults within the pool was based on simple binomial probability formulas that assumed that defaults would be fully independent across borrowers Once a default probability had been estimated for loans in a pool, the probabilities of potential multiple defaults within the pool was based on simple binomial probability formulas that assumed that defaults would be fully independent across borrowers To account for the obvious flaw that defaults are likely to be correlated, Moodys introduced an adjustment called Diversity Scoring To account for the obvious flaw that defaults are likely to be correlated, Moodys introduced an adjustment called Diversity Scoring In 1999, Northfield published a research paper criticizing BET and Diversity Scoring based on a client request In 1999, Northfield published a research paper criticizing BET and Diversity Scoring based on a client request

26
Moodys Diversity Scoring To account for default correlation, Diversity Scoring reduced the assumed number of issues in a loan pool To account for default correlation, Diversity Scoring reduced the assumed number of issues in a loan pool For example, if you had 70 loans in a pool, you might count that as 40 independent loans For example, if you had 70 loans in a pool, you might count that as 40 independent loans Moodys broke firms into 32 industries Moodys broke firms into 32 industries 2 credits in the same industry counted as 1.5 2 credits in the same industry counted as 1.5 10 credits in the same industry counted as 4 10 credits in the same industry counted as 4 Implicitly there is an assumption that defaults are correlated within industries, but never across industries Implicitly there is an assumption that defaults are correlated within industries, but never across industries Completely ignores potential for pervasive effects of recession, war or other systemic influences Completely ignores potential for pervasive effects of recession, war or other systemic influences Although Moodys largely abandoned BET in 2005, many institutions such as AIG continued to use the method Although Moodys largely abandoned BET in 2005, many institutions such as AIG continued to use the method

27
The Secret Formula That Destroyed Wall Street Cover story in WIRED magazine, March 2009 Cover story in WIRED magazine, March 2009 Refers to the Gaussian Copula approach for estimating default risk across a pool of loans, from Li (2000) Refers to the Gaussian Copula approach for estimating default risk across a pool of loans, from Li (2000) Allows for closed form calculation of marginal risks as more and more loans are added to the pool to be securities Allows for closed form calculation of marginal risks as more and more loans are added to the pool to be securities Requires an assumption of the expected correlation of defaults Requires an assumption of the expected correlation of defaults The problem is credit risky instruments have high skew in the payoff distribution, so the joint distribution will be Gaussian under the Central Limit Theorem only for very large numbers of independent events The problem is credit risky instruments have high skew in the payoff distribution, so the joint distribution will be Gaussian under the Central Limit Theorem only for very large numbers of independent events Even a small degree of correlation calls the method into question Even a small degree of correlation calls the method into question

28
The Problem of Higher Order Dependence Imagine you want to allocate money to two hedge funds based on traditional MPT Imagine you want to allocate money to two hedge funds based on traditional MPT The two portfolio managers happen to have offices in the same building and meet for coffee every morning The two portfolio managers happen to have offices in the same building and meet for coffee every morning During conversation, they flip a coin. If the coin comes up heads they hold the identical portfolio for that day. If it comes up tails they go long/short against each other During conversation, they flip a coin. If the coin comes up heads they hold the identical portfolio for that day. If it comes up tails they go long/short against each other If the coin is fair, the time series of their portfolio returns will be zero If the coin is fair, the time series of their portfolio returns will be zero It varies daily from +1 to -1. averaging zero It varies daily from +1 to -1. averaging zero Being independent implies zero correlation, but zero correlation does not imply independence Being independent implies zero correlation, but zero correlation does not imply independence

29
We Go Blindly Forward with the Gaussian Copula Investment banks love the Gaussian copula because now you can get joint default probabilities over any number of loans with the estimation of a single number, the default correlation Investment banks love the Gaussian copula because now you can get joint default probabilities over any number of loans with the estimation of a single number, the default correlation The rating agencies such as Moodys and S&P go along and rate based on this method The rating agencies such as Moodys and S&P go along and rate based on this method The problem is where to get the default correlation assumption, since actual defaults were rare events, so statistical estimation from historical data is questionable The problem is where to get the default correlation assumption, since actual defaults were rare events, so statistical estimation from historical data is questionable Bankers used observable correlations from changes in spreads in the credit default swap market Bankers used observable correlations from changes in spreads in the credit default swap market

30
CDO/CDS Default Correlations Assessing default correlations from credit swap curves and CDO trading was horrendously faulty Assessing default correlations from credit swap curves and CDO trading was horrendously faulty Once CDOs and CDO 2 could be written on generic ABS index results instead of specific pools, they were a form of legalized gambling Once CDOs and CDO 2 could be written on generic ABS index results instead of specific pools, they were a form of legalized gambling The volumes in the CDO market were many times the volume of actual underlying loans against which to hedge credit risk, creating severe pricing distortions The volumes in the CDO market were many times the volume of actual underlying loans against which to hedge credit risk, creating severe pricing distortions The CDO/CDS markets were dominated by a few large players such as AIG, further distorting economic pricing relationships The CDO/CDS markets were dominated by a few large players such as AIG, further distorting economic pricing relationships

31
Summary The global financial crisis has many contributing factors, but the largest single contributor was the horrendous performance of fixed income credit ratings from the major rating agencies The global financial crisis has many contributing factors, but the largest single contributor was the horrendous performance of fixed income credit ratings from the major rating agencies In some cases, the quality of ratings was severely upward biased by business in considerations In some cases, the quality of ratings was severely upward biased by business in considerations In many cases the contributing factors were simply poor quantitative analysis in which mathematical convenience was allowed to take precedence over the conceptual rigor of the models In many cases the contributing factors were simply poor quantitative analysis in which mathematical convenience was allowed to take precedence over the conceptual rigor of the models The shortcomings in the analytical methods applied to the RMBS, CDO and CDS markets were easily observed by those who were relatively free of conflicts of interest The shortcomings in the analytical methods applied to the RMBS, CDO and CDS markets were easily observed by those who were relatively free of conflicts of interest

Similar presentations

OK

CHAPTER 4 Background on Traded Instruments. Introduction Market risk: –the possibility of losses resulting from unfavorable market movements. –It is the.

CHAPTER 4 Background on Traded Instruments. Introduction Market risk: –the possibility of losses resulting from unfavorable market movements. –It is the.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google