External and Internal Credit Ratings

Welcome to the World of Credit Ratings!

Hi there! Welcome to one of the most practical and essential chapters in the Valuation and Risk Models section. Whether you are looking at a giant corporation or a local bank, everyone wants to know one thing: "Will I get my money back?"

Credit ratings provide a standardized answer to that question. In this chapter, we will explore how external agencies and internal bank models measure the "creditworthiness" of borrowers. Don't worry if this seems like a lot of jargon at first—we will break it down piece by piece with simple analogies and clear steps.

1. What is a Credit Rating?

At its heart, a credit rating is simply an opinion. It is an assessment of the creditworthiness of a borrower (an individual, a company, or even a country) regarding a specific financial obligation.

The Analogy: Think of a credit rating like a student's Grade Point Average (GPA). A student with a 4.0 GPA is considered "high quality" and likely to pass future tests. A student with a 1.5 GPA is "high risk" and might fail. Credit ratings do the same for companies: they tell investors how likely the company is to fail (default) on its debt.

External vs. Internal Ratings

• External Ratings: These are provided by independent companies called Credit Rating Agencies (CRAs), such as Standard & Poor’s (S&P), Moody’s, and Fitch. They sell their research and ratings to the public and investors.
• Internal Ratings: These are developed by banks and financial institutions for their own use. They help banks decide whether to give you a loan and how much interest to charge.

Quick Review: External ratings are for the public market; Internal ratings are for the bank's private decision-making.

2. The Rating Scales: Making Sense of the Letters

Each agency has its own "alphabet soup" of ratings. While they look slightly different, they generally mean the same thing. The most important distinction you need to know for the FRM exam is the line between Investment Grade and Non-Investment Grade (also called "Speculative" or "Junk").

Key Rating Categories:

1. Investment Grade: These are "safe" bets.
- S&P/Fitch: AAA, AA, A, BBB
- Moody’s: Aaa, Aa, A, Baa

2. Speculative Grade (High Yield/Junk): These are "risky" bets.
- S&P/Fitch: BB, B, CCC, CC, C, D
- Moody’s: Ba, B, Caa, Ca, C

Important Point: The "cutoff" line is BBB- (S&P) or Baa3 (Moody's). Anything below this is considered speculative. Many pension funds are legally forbidden from owning "junk" bonds, so if a company is downgraded from BBB- to BB+, it is a huge deal!

Memory Trick: Think of AAA as "Awesome And Ample" safety. Think of C as "Close to Crash."

3. Through-the-Cycle (TTC) vs. Point-in-Time (PIT)

This is a favorite topic for exam questions! Agencies and banks use two different philosophies when assigning a rating.

Point-in-Time (PIT)

A PIT rating reflects the borrower’s current condition right now. It accounts for the current phase of the business cycle (recession or boom).

• Characteristics: Highly volatile. If the economy dips for three months, the rating dips too.
• Analogy: Your weight on a scale this morning after a big holiday dinner. It tells you exactly how things look right now.

Through-the-Cycle (TTC)

A TTC rating focuses on the long-term, structural ability of the borrower to pay. It tries to "look past" the temporary ups and downs of the economy.

• Characteristics: Stable. Ratings only change if the company’s fundamental business model changes. Most external agencies (S&P/Moody's) use the TTC approach.
• Analogy: Your average weight over the last three years. It doesn't change just because you had one big meal; it only changes if you permanently change your lifestyle.

Common Mistake: Students often think PIT is better because it is "current." However, for long-term investors, TTC is often preferred because it prevents constant, knee-jerk buying and selling of bonds based on temporary news.

4. Rating Transitions and the Transition Matrix

Ratings aren't permanent. A company that is A today might become BBB next year. This is called a Rating Transition.

To track this, we use a Transition Matrix. This table shows the probability of a company moving from one rating to another over a specific period (usually one year).

• The rows represent the starting rating.
• The columns represent the ending rating.
• The diagonal cells show the probability of the rating staying the same. (In a stable world, the diagonal numbers should be the highest!)

Key Formula: The probability of default, \( P(D) \), is usually the last column in the matrix (the transition to "D").

Example: If a row starts at 'BBB' and the cell under the 'D' column is 0.002, it means there is a 0.2% chance a BBB-rated firm will default within the year.

5. Internal Rating Systems (The Bank's View)

Banks can't just rely on S&P or Moody’s. Why? Because many small businesses don't have external ratings! Under the Basel Framework, banks develop their own Internal Ratings-Based (IRB) systems.

The Three Key Ingredients:

To calculate the risk of a loan, banks look at:

1. Probability of Default (PD): What are the chances they won't pay?
2. Loss Given Default (LGD): If they default, what percentage of the money will we actually lose? (e.g., if we can sell their building for 40% of the loan, the LGD is 60%).
3. Exposure at Default (EAD): How much money is owed to us at the exact moment they stop paying?

Expected Loss (EL) Formula: \[ EL = PD \times LGD \times EAD \]

Don't worry, this formula is simpler than it looks! It’s just (Chance of failing) x (Amount we lose if they fail) x (Total amount owed).

6. Hazards and Limitations of Ratings

While credit ratings are helpful, they aren't perfect. You should be aware of these common criticisms:

• Lagging Indicators: Ratings often change after the market has already realized a company is in trouble. (Remember the 2008 financial crisis!)
• Conflicts of Interest: The "Issuer-Pay" model. Since companies pay the agencies to rate them, there is a fear that agencies might give higher ratings to keep their "customers" happy.
• Pro-cyclicality: If agencies downgrade everyone during a recession, it can make the recession worse because banks stop lending.

Did you know? During the 2008 subprime mortgage crisis, many complicated products were rated AAA (the highest possible safety) but were actually full of very risky loans. This led to many reforms in how agencies operate today.

Summary and Key Takeaways

1. Ratings are Opinions: They measure the likelihood of default, not the price of the bond.

2. The Crossover: BBB- (S&P) or Baa3 (Moody's) is the line between "Investment Grade" and "Junk."

3. TTC vs. PIT: TTC is long-term and stable; PIT is current and volatile.

4. Expected Loss: Remember the formula \( EL = PD \times LGD \times EAD \).

5. Transitions: A transition matrix helps us predict how ratings will change or "migrate" over time.

You've got this! Credit ratings might seem like a lot of letters and numbers, but they are just a way to quantify trust. Keep practicing with the transition matrices, and you'll be an expert in no time!