Question: what is the formula to calculate the transition probability?
Answer: The formulas for the transition probabilities are p11(t) = eat, p12(t) = bueft + qeat, and so on. In general, if i is a death state (that is, an absorbing state) then pii(t) = 1. So, for this model,p44(t) is actually 1, and the pz in the formula for p34(t) can also be replaced by 1.