1.4b – Scope, Schedule, and Cost: The Triple Constraint

Sarah quickly learns that scope, schedule, and cost are interconnected. Every project has constraints on all three, and trade-offs are unavoidable. The relationship between these three has evolved as organizations adopt agile and hybrid approaches.

1.4b.1 The Classic Triple Constraint

In traditional project management, the "triple constraint" is:

• Scope: What will be delivered?
• Schedule: When will it be delivered?
• Cost: How much will it cost?

The classic view: If you fix two of these, the third is determined.

• Fix scope and schedule → cost is determined (spend whatever it takes)
• Fix cost and schedule → scope is determined (deliver only what fits)
• Fix cost and scope → schedule is determined (takes as long as it takes)

1.4b.2 Modern View: Constraints and Priorities

• Predictive projects: The triple constraint holds strongly. Scope, schedule, and cost are baseline constraints.
• Agile projects: The model is inverted.
  • Fixed: Time (sprints) and Cost (team capacity)
  • Flexible: Scope (features adjust based on priority)
• Hybrid projects: A mix. Program level might have fixed scope/date, while team level has flexible scope within sprints.

🔒 Scope (Fixed)

🔄 Cost (Estimated)

🔄 Time (Estimated)

Plan-Driven

Scope is defined first. Time and Cost are estimated to meet it.

1.4b.3 The Iron Triangle vs. The Diamond

Sarah realizes that scope, schedule, and cost are not the only success criteria. Modern thinking adds:

• Quality: Does it work as required?
• Value: Does it deliver the intended benefits?
• Risk: Are we managing uncertainty effectively?

INFO

You cannot optimize for schedule and cost alone while ignoring quality or value.

1.4b.4 Scope Definition: The Foundation

Clear scope definition reduces surprises and conflict.

1. Product scope: Features and characteristics of the deliverable.
2. Project scope: Work done to create the product.
3. Out of scope: Explicit exclusions to prevent scope creep.

Predictive: Defined in detail upfront (WBS, requirements spec). Agile: Emerges over time (Product Vision, prioritized Backlog).

1.4b.5 Schedule: Sequencing and Dependencies

1. Identify activities: What work needs to be done?
2. Sequence activities: What depends on what? (Finish-to-Start, etc.)
3. Estimate duration: How long will each step take?
4. Build the schedule: Critical Path Method (CPM) and Gantt charts.

Predictive: Detailed master schedule with clear milestones. Agile: Timeboxed iterations (sprints) with velocity-based planning.

1.4b.6 Cost and Budget: Tracking and Controlling

Predictive:

• Estimate costs for each activity.
• Develop a cost baseline (S-curve).
• Track actuals and analyze variance (Earned Value).

Agile:

• Burn rate: Fixed cost per sprint (team capacity).
• Budgeting: "How many sprints can we afford?"

1.4b.7 Managing the Triangle: Trade-off Decisions

When you cannot have everything:

1. Identify the true constraint: What is non-negotiable?
2. Explore options: Extend schedule, reduce scope, or increase budget.
3. Understand trade-offs: What is the impact of each choice?
4. Decide explicitly: Make the choice with stakeholders.

1.4b.8 On the Exam: Scope, Schedule, Cost

Red Flag Answers:

• Promising everything without discussing trade-offs.
• Making scope changes silently.
• Cutting quality to hit a deadline.

Good Answers:

• Identifying fixed constraints.
• Communicating trade-offs clearly.
• Updating baselines after an agreed change.

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Formula Check

For detailed formulas on Critical Path and Earned Value, see Appendix B: Key Formulas and Definitions.