Assessing Credit Risk in Bonds

Anna is a portfolio manager overseeing a diversified investment portfolio. She is currently assessing the credit risk associated with her bond investments. Credit risk is primarily the risk that a bond issuer will default on its obligation to pay interest and principal. To mitigate this risk, Anna considers various factors that can impact creditworthiness, such as the issuer's financial health and industry conditions. In this context, what is the primary measure that Anna should focus on to evaluate credit risk?