Work Package Resources: Aggregation and Estimation in the WBS

PMBOK v8 Definition

A work package is the work defined at the lowest level of the work breakdown structure (WBS) for which cost and duration can be estimated and managed. Resource activity in a work package can be aggregated to determine the estimated resources for each work package, each WBS branch, and the entire project. The amount of detail and the level of specificity of the resource requirement descriptions can vary by application area.

Why It Matters for the Exam

This concept appears frequently in PMI exam questions about scope management, resource estimation, and cost aggregation. You will encounter it in situational questions where you must identify the correct level of the WBS for estimating resources, as well as in definition-based questions about the relationship between work packages, control accounts, and resource requirements.

Key Points to Remember (for the exam)

• Work Package Definition: The lowest level of the WBS where cost and duration are estimated and managed
• Resource Aggregation: Resources from individual work packages are aggregated upward to determine estimated resources for each WBS branch and the entire project
• Unique Identifier: Each work package has a unique identifier that provides structure for hierarchical summation of costs, schedule, and resource information
• Code of Accounts: The identifiers form a code of accounts for hierarchical summation
• Control Account Relationship: Each work package is part of a control account; a control account has two or more work packages, but each work package is associated with a single control account
• Resource Requirements Documentation: May include assumptions made in determining which types of resources should be applied, their availability, and what quantities are needed
• Level of Decomposition: Guided by the degree of control needed to effectively manage the project; detail varies depending on project size

Typical PMI Exam Example

A project manager is estimating resources for a construction project. The WBS has been decomposed to the work package level for foundation work, framing, and electrical systems. The project manager estimates the resources needed for each work package individually, then aggregates these estimates to determine total resources required for the entire project. Which concept does this describe?

Answer: Work package resource aggregation

PMI Exam Traps

• Trap: Confusing work package with planning package Reality: A work package is the lowest level where cost and duration are estimated; a planning package is a placeholder in a control account for work not yet decomposed to work package level

• Trap: Thinking each control account contains only one work package Reality: A control account has two or more work packages, though each work package is associated with a single control account

• Trap: Assuming resource requirements are always detailed and specific Reality: The amount of detail and level of specificity of resource requirement descriptions can vary by application area

• Trap: Confusing work package estimation with activity estimation Reality: Work package estimation is at the WBS lowest level; activities are further decomposition of work packages for scheduling purposes

Important PMI Connections

Quick Review Questions

1. What is the lowest level of the WBS for which cost and duration are estimated and managed?

2. How are work package resources used to determine total project resource estimates?

3. How many work packages can a single control account contain?

4. What information may be included in resource requirements documentation beyond the types and quantities of resources?

5. What guides the level of decomposition of work packages in a WBS?

PMBOK v8 Reference

Section 5 – Tools and Techniques (Work Breakdown Structure content)