So far we have described a rather intuitive way of combining individual views in a portfolio. Top-down and bottom-up analyses have determined the overall strategy for the portfolio, spread class and sector selection and finally issuer weightings. This qualitative methodology does not require estimates of returns, risks and correlations between the investments, and therefore is easy to implement. Yet, it is not able to capture the full benefits of diversification and to tailor the expected risk/return profile of the portfolio to the preferences of the investor. Since the seminal work of Markowitz (1952), diversification is a central tenet of modern investment theory. In the context of credit portfolios it plays a crucial role, because it helps to control downside risk arising from single issuer credit events. Since the mid-1990s debt-financed M&A activities, share buybacks, and the introduction of new technologies have fueled the new issue pipeline and broadened the corporate bond universe. Meanwhile, the European corporate bond market offers sufficient market breadth and depth for institutional investors to construct thoroughly diversified portfolios. If the portfolio manager is capable of quantifying the risk and return characteristics of his investment alternatives, portfolio optimization approaches present a formalized and thus objective way of deriving investment recommendations. This applies irrespective of the performance target of the investor. Portfolio optimization can be used with respect to portfolios that are managed in absolute risk/return terms as well as portfolios that are managed relative to a benchmark index. Various constraints can be included, for example a short sales restriction for real money investors, maximum concentration limits or esired duration ranges.

Similar to the level of interest rates itself the slope of the yield curve also is an indicator for the economic environment. Generally, the slope of the yield curve is seen as a good proxy for future economic growth and corporate profits.

Steep yield curves imply that future rates are expected to be higher than at present. Asteep 2s10s slope and a further steepening of the 2s10s slope in the past often have been followed by positive excess returns of corporate bonds. Usually, one observes a steepness in this part of the curve at the end of a recession and at the start of an expansion. When the expansion finally materializes the curve flattens, and inflation concerns cause central banks to raise interest rates. In this environment, credit usually suffers, and investors should be particularly cautious when overweighting cyclical credits.

Globally, the low interest rate environment in the first years of the new millennium has spurred investors’ interest in credit as a way to boost returns. However, one has to be aware that there is a correlation between the level of interest rates, the slope of the yield curve and credit spreads because both the yield curve and credit spreads reflect the state of the economy.

Since they are driven by expectations about the same underlying factor, the relation between the yield curve and credit spreads has an impact on top-down driven asset allocation and duration decisions.

In the past, credit spreads have been closely correlated with interest rates. There is typically a negative correlation between spreads and the level of interest rates. As interest rates increase due to an improving outlook for future economic growth and rising price pressure, credit quality tends to improve because firms have opportunities to strengthen their future earnings and cashflows. Similarly, a flatter money market slope (2 years–6 months) is usually positive for credit spreads because it indicates better economic conditions. In a difficult economic environment, such as at the trough of the recession, the money market curve tends to be very steep and credit usually underperforms treasuries, especially at the long end.