Systematic risk, also known as market risk or non-diversifiable risk, is the risk that affects all sectors and cannot be eliminated through diversification. It is influenced by macroeconomic factors such as inflation rates, exchange rates, and political instability. Default correlation is a measure of the likelihood of joint defaults, and it is one way of representing high systematic risk. When default correlation is high, it means that the likelihood of multiple entities defaulting at the same time is high, which is a characteristic of systematic risk. Therefore, default correlation is equivalent to systematic risk.

Choice B is incorrect. Credit Value at Risk (VaR) is a measure of the worst expected loss over a given time period under normal market conditions at a certain confidence level. It does not represent systematic risk, but rather quantifies potential losses in the value of a credit risky portfolio.

Choice C is incorrect. Tranche thinness refers to the situation where there are too few underlying assets in an investment tranche, which can lead to higher default risk if one or more of those assets fail. This concept relates more to idiosyncratic risk than systematic risk.

Choice D is incorrect. Granularity refers to the degree of detail or specificity in data or information sets, and it's not directly related to systematic risk which affects an entire market segment.

Things to Remember

• Default correlation is the metric most directly associated with portfolio credit risk, as it signifies the relationship between defaults of different entities within the portfolio.
• Understanding the significance of default correlation is vital since high correlations imply that the entities are more likely to default together, hinting at an elevated level of systematic risk in the portfolio.