Which is NOT a measure commonly used by top-down portfolio managers to assess credit quality?

Top-down portfolio managers focus on macroeconomic factors and broad industry analysis when making investment decisions, especially in the context of credit risk assessment. They utilize several measures to assess credit quality, which include evaluating the average credit quality of the bonds in their portfolio, analyzing the average spread duration to determine sensitivity to interest rate changes, and using the average option-adjusted spread (OAS) as a metric to assess the additional yield an investor receives over the benchmark yield for taking on credit risk.

The standard deviation of returns, however, is primarily a measure of volatility and risk associated with the portfolio's returns rather than a direct assessment of credit quality. While standard deviation can provide insight into the risk profile of a portfolio, it does not specifically relate to the creditworthiness of the underlying securities. Hence, it is not typically employed by top-down portfolio managers as a primary metric for assessing credit quality, making it the correct choice in this scenario.