Conceptual / approximate estimating methods in early project stages (Select the method(s) commonly used to prepare quick, order-of-magnitude estimates.)

Introduction / Context:
At the conceptual stage, detailed quantities are unavailable. Estimators rely on high-level cost models to obtain fast, defensible budgets. Several benchmarked methods exist for different facility types and scopes.

Given Data / Assumptions:

• Scope definition is preliminary.
• Historical cost indices and normalization factors (location, time) are applicable.
• Accuracy band is broad (order of magnitude).

Concept / Approach:
Four families of conceptual methods see frequent use: base unit (cost per primary unit delivered), cost per function (cost per capacity or performance measure), cost per square metre (useful for buildings), and cost per linear unit (for line-like assets). Each supports rapid comparison of alternatives and budgetary screening before detailed design.

Step-by-Step Solution:
1) Match method to asset type and dominant driver (area, length, capacity, count).2) Normalize for location, escalation, and scope differences.3) Apply appropriate allowances (contingency, design fees, overheads).4) Validate against benchmarks from similar completed projects.

Verification / Alternative check:
Professional estimating guides list these families as standard tools for Class 4–5 estimates (early phase).

Why Other Options Are Wrong:
Options a–d are each valid methods; no single one dominates all contexts. Therefore the inclusive choice is correct.

Common Pitfalls:
Using area rates where capacity is the true cost driver; ignoring perimeter-dependent costs; failing to adjust historical data for market conditions.

Final Answer:
All of these