scopeeconomics
Make scope, quantities, rates and exclusions traceable to a defined issue.
The basis of estimate records the position that the number represents. Another estimator should be able to identify the scope, source information, price basis and important assumptions without reconstructing them from scattered emails. The level of detail should suit the purpose of the estimate.
Write specific statements. “Access included” is less useful than explaining the access method, duration and package carrying the allowance. Where a cost sits elsewhere in the model, record the reference. This reduces the chance that an interface will be omitted or priced twice.
A quantity may describe installed work, purchased material or a supplier’s payment unit. State which is being used. Then check that the rate covers the same work. Multiplying an installed length by a supply-only rate does not produce a complete installed cost.
Record the price date and currency. A quotation from another period can be useful evidence, but it needs review before being used as a current input. Separate any adjustment from the original source so that a reviewer can see both the evidence and the judgement.
A scope exclusion is not automatically covered by contingency. If a known item is intentionally outside the estimate, say so. If it is required but has not yet been priced, identify the allowance or open action. These are different estimating positions.
At issue, keep the model, source register and basis together under a clear reference. When revising the estimate, explain which assumptions changed. This makes the document useful for future comparison instead of leaving it as a description of a model that no longer exists.
An illustrative 800 m installation has a verified composite rate of £35 per installed metre. Mobilisation is a separate £5,000 allowance. Tax and design fees are outside this example.
| Cost item | Calculation | Amount |
|---|---|---|
| Installed work | 800 m × £35/m | £28,000 |
| Mobilisation | Separate fixed allowance | £5,000 |
| Defined package total | £28,000 + £5,000 | £33,000 |
Original example with illustrative GBP inputs. The exclusions remain outside this total.