Existence Risks

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An existence risk is an activity which may or may not occur. By default:

  • All activities start out with an existence probability of 100%, meaning they will occur in every iteration during the simulation
  • When an existence probability of less than 100% is entered, the duration is zeroed out for those iterations that it's sampled as not occurring
ExampleOption 1Option 2
Schedule resubmittalIncluding in the duration range results in an overly pessimistic distribution on the submittal activitySuccessor activity to schedule submittal with 0 day duration, existence probability <100%
Risk of encountering contaminated soil during excavationIncluding as a risk impact may conflate weather modelingInsert activity with 0 day duration, existence probability <100%

Designating Existence Risks

  1. Click the Ranging  icon.
  2. Click the View button above the top list and choose Duration and Cost.
  3. Scroll to the desired activity.
  4. Enter a value less than 100% in the Existence Probability column.


To turn on the Existence Probability column, see Customizing Columns.

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Existence Probability: the percent of iterations an activity will occur. When it occurs, the activity's duration is sampled from its range. When it doesn't occur, its duration is zeroed out for that iteration.