A common error in models is when the branch probabilities do not sum to 1 (or 100%).
There is a feature in TreeAge Pro where you can automatically normalize the branch probabilities of a chance node to ensure this error does not occur.
- Probability expressions:
- branch A prob is pA
- branch B prob is pB
- branch C prob is #
- Scenario 1, no normalization needed.
- pA = 0.2
- pB = 0.3
- pC = # , and would calculate to 0.5
- Scenario 2, normalization needed.
- pA = 0.5 - normalized to 0.5/(0.5+0.6)
- pB = 0.6 - normalized to 0.6/(0.5+0.6)
- pC = #, and would calculate to 0. Without normalization, this would create an error because (0.5 + 0.6) > 1.
This is a relatively blunt tool, but it will automatically reduce the probabilities (including the # towards 0) as your probabilities (pA and pB) go up to the point where "un-normalized" probabilities exceed 100%.
To use this function, right-click on the chance node and choose Change Coherence > Normalize Probabilities from the context menu.