When to use it
Use analogous estimates early, then add measurable quantities and calibrated rates as scope becomes clearer.
Do not call a convenient ratio a validated model; scale, complexity and omitted work can break it.
Apply it
Only valid over the range and work boundary for which the rate is supported. Add separately identified work rather than burying it in the rate.
- Define the scope and the decision the estimate supports.
- Choose comparable evidence and adjust for material differences.
- Document the range, exclusions and how actuals will update the estimate.
An example in practice
Estimate a rollout using observed effort per comparable installation, then separately allow for integration and training that the historical rate excluded.
Source & credit
Standard estimating practice; the cited guide documents use rather than claiming invention.
GAO: Cost Estimating and Assessment Guide
This explanation and example are independently written. The source is a reading reference; linking it does not grant permission to reuse its text, figures or assessments.