... for Aaa-rated bonds~it is statistically insignificant for long-maturity and medium-maturity Aaa-rated bonds! and strengthens as credit quality falls. The relation between yield spreads and the ... I adjust the variance-covariance matrix of the estimated coefficients for generalized heteroskedasticity and two lags of moving average residuals. The results indicate that an increase in the ... in spreads for four business-sectorcategories ~all sectors’ bonds, industrial-sector bonds, utility-sector bonds, and financial-sector bonds!, four rating categories ~Aaa, Aa, A, and Baa!,and...