Core idea: Sensitivity analysis changes one or more inputs and observes how the result or ranking responds.
When this model is useful
Use it after a base model to distinguish robust conclusions from choices that depend on one uncertain estimate.
The method is most useful when the question, alternatives and time horizon are stated before calculations begin. It should clarify tradeoffs and identify which assumptions deserve attention, not merely produce a score.
Inputs and evidence
A base-case model, credible input ranges, relationships between variables and a clear decision metric or option ranking.
Use consistent units, definitions and periods across options. Mark estimates clearly, record their source and use ranges when precision is not supported. Evidence should be proportionate to the cost, risk and reversibility of the choice.
Step-by-step method
Vary important inputs one at a time, test key pairs together, calculate switching values and focus further research on assumptions that can reverse the decision.
- Write the decision question and accountable owner.
- List realistic alternatives and eliminate any that fail hard constraints.
- Collect evidence and separate verified facts from assumptions.
- Run a base case and at least one downside test.
- Record the chosen option, accepted tradeoffs and review triggers.
Practical example
If a purchase is preferable only when useful life exceeds seven years, the seven-year point is a critical breakpoint that deserves better evidence.
The point of the example is not the exact numbers. It is the discipline of using the same boundaries for every option and making the decision drivers visible.
Common mistake and limitation
Ranges should come from history, contracts, research or explicit stress tests, not numbers selected to defend a preferred conclusion.
Review whether the result changes under reasonable alternative assumptions. A close or fragile ranking should be presented as such rather than converted into false certainty.
Questions to ask before deciding
- What evidence would change the preferred option?
- Which consequence is missing because it is difficult to measure?
- Could a threshold or constraint override the numerical result?
- Who receives the benefits and who bears the costs or risk?
- When should the decision be reviewed?
Professional context: Legal, tax, investment, safety, medical, engineering and regulated decisions require qualified, jurisdiction-specific advice.