Before revision: Bond rating Transition Probability Matrices (TPMs) are built over a one-year time-frame and for many practical purposes, like the assessment of risk in portfolios  , one needs to compute the TPM for a smaller time interval.
After revision: Bond rating Transition Probability Matrices (TPMs) are built over a one-year time-frame and for many practical purposes, like the assessment of risk in portfolios , one needs to compute the TPM and probabilities of default over a smaller time interval.