Applies to: @RISK for Excel version 5.x and Up

 

@RISK Message: “Checking precedents”

Is something wrong with my model?
No. This behavior is expected.

• The delay occurs because Precedent Checking, also called Smart Sensitivity Analysis, runs before the first simulation iteration.

What is Precedent Checking (Smart Sensitivity Analysis)?
Precedent Checking analyzes which @RISK inputs actually affect each RiskOutput.

• Its purpose is to prevent inputs that do not influence an output from incorrectly appearing in regression and sensitivity results such as tornado graphs.

Why was this feature added?
In earlier versions of @RISK, inputs that were correlated but not actually used in calculations could appear to have equal impact on outputs.

• For example, two inputs might be perfectly correlated, but only one is used in calculating a RiskOutput.
• Older versions would show both as equally influential.
• Smart Sensitivity Analysis correctly identifies and excludes the unused input.

Why does this slow down the simulation start?
Before the simulation begins, @RISK must trace the entire precedent tree to determine which inputs affect which outputs.

• In large or complex models, this analysis can take significant time.

How can I speed this up?
You can reduce input data collection by setting Collect to None for some or all inputs.

This speeds up precedent checking but prevents those inputs from appearing in sensitivity analysis.

• You can still collect statistics by designating certain inputs as outputs.
• You can also disable Smart Sensitivity Analysis for a specific model by opening Simulation Settings, selecting the Sampling tab, and setting Smart Sensitivity Analysis to Disabled.
  • To change the default for all models, go to Utilities » Application Settings and adjust the Default Simulation Settings.
  • Another option is to exclude specific inputs using RiskMakeInput() functions so they are ignored during precedent tracing.

Does Smart Sensitivity Analysis have limitations?
Yes. Some Excel formulas cannot be reliably traced because their references can change at runtime or are too complex.

• These include
  • INDIRECT(), OFFSET(), INDEX() when returning references
  • VLOOKUP() and HLOOKUP(), 3-D references across worksheets
  • certain structured table references
  • references to external workbooks, and
  • Internet-based references.
• In these cases, calculations still run correctly, but @RISK cannot trace precedents.

What happens if my model uses one of these formulas?
When you start the simulation, a message such as “could not be parsed” or “invalid formula” may appear.

• Click Yes to proceed.
• To prevent future messages, either modify the formula if possible or disable Smart Sensitivity Analysis for the model via Simulation Settings on the Sampling tab.