# How to vary transitional probability which enters a specific state?

This is my Markov model, but I do not know how to use treeage to express it. I entered obstacle when expressing the heath states from First year of gastric cancer to Fifth year of gastric cancer, because the transitional probability from 1st year of GC to 2nd year of GC is 0.5, while the transitional probability from 2nd year of GC to 3rd of GC is 0.4 and so on.

So, I think I can set a time-dependent variable, but this variable should start when this person enters the first year of gastric cancer, not when this person enters the very beginning progarmme.

Many thanks for the dissussion and answers!

1 comment
• You can probably use tunnels to achieve this.

You can setup an health state as a tunnel state to track the number of cycles patients have spent within that state.

1. Set the tunnel max for the health state to the lowest value possible to account for the differences in values. For example, if the value changes for the last time in the 5th cycle, set the tunnel max to 5.
2. Reference the keyword _tunnel in a formula for probabilities, etc. for anything that change by cycle in state.

More details on tunnels are available in the software documentation (menu: Help > Help).