Applies to:
@RISK 6.x and Up, Professional and Industrial Editions
@RISK for Project 4.x (using the RiskBranch function)

 

Why Do Some Outputs Show "Error" in Probabilistic Branching Simulations?

Question:
In my @RISK simulation with probabilistic branching, some outputs show "Error" for certain iterations instead of a data point. What’s wrong?

Answer:
This behavior is by design.

• In each iteration, the branching function selects one branch. Branches that are not chosen are zeroed out, meaning affected tasks and their descendants are skipped.

• Outputs related to zeroed-out tasks return "Error" instead of a value. This ensures that skipped branches do not skew summary statistics.

Example:

• Task A branches 70% to B1 and 30% to B2.

• For 100 iterations:

  • B1 finish date: 70 values, 30 errors

  • B2 finish date: 30 values, 70 errors

• Only the non-error outputs reflect the behavior when that task is included.

Note:
If B1 and B2 are on the same path (e.g., B1 is a predecessor of B2), B2 will always execute, while B1 will show errors in iterations skipped due to branching.

This ensures accurate modeling of probabilistic paths in your project.