The relative difference in yield to maturity (YTM) between two bonds (bond issues) or two classes of bonds with similar maturities. It is the ratio of the yield spread to the yield of the reference bond.  Suppose there are two bonds: bond X and bond Y, relative yield spread is computed as follows:

Relative yield spread = (yield on bond X – yield on bond Y)/yield on bond Y

Bond Y represents the reference bond (benchmark) against which bond X is measured (in basis points). For example, on some date, the yield on the 10-year on-the-run Treasury issue was 4.70% and the yield on a single A rated 10-year industrial bond was 6.50%. The relative yield spread (where the Treasury issue is the reference bond) would be:

Relative yield spread = (6.50% – 4.70%)/4.70% = 0.3829

The relative yield spread is 0.3829 or 38.29% of the yield of the reference bond.