Critical Chain Method

Critical Chain Method: A Comprehensive Guide for PMI-SP Exam

Understanding the Critical Chain Method (CCM)

The Critical Chain Method (CCM) is an advanced project scheduling technique developed by Dr. Eliyahu Goldratt as an application of his Theory of Constraints. It's a crucial concept in the PMI Scheduling Professional (PMI-SP) certification and appears frequently on the exam.

Why Critical Chain Method is Important

CCM addresses key limitations of traditional Critical Path Method (CPM) by:
- Focusing on resource constraints rather than just task dependencies
- Managing uncertainty through strategic buffer placement
- Combating common scheduling problems like student syndrome (delaying work until deadlines approach) and Parkinson's Law (work expanding to fill available time)
- Improving project delivery predictability

What is the Critical Chain Method?

Critical Chain Method is a scheduling technique that:
- Identifies the longest sequence of tasks considering both dependencies and resource constraints
- Removes individual task safety margins and places them strategically as buffers
- Uses buffer management to monitor and control project progress
- Emphasizes resource availability as a primary constraint in project scheduling

How Critical Chain Method Works

1. Create a baseline schedule
- Develop a network diagram with task dependencies
- Assign resources to activities
- Use aggressive (50% probability) duration estimates

2. Identify resource constraints
- Look for resource conflicts and overallocations
- Level resources to create a resource-feasible schedule

3. Identify the critical chain
- This is the longest path considering both dependencies and resource constraints
- Unlike critical path, critical chain accounts for resource limitations

4. Add buffers
- Project buffer: Added at the end of the critical chain to protect project completion date
- Feeding buffers: Added where non-critical chains feed into the critical chain
- Resource buffers: Time alerts to ensure critical chain resources are available when needed

5. Monitor buffer consumption
- Track how quickly buffers are being used
- Take corrective action when buffer consumption exceeds project progress

Key Differences from Critical Path Method

- CPM focuses on task dependencies; CCM adds resource dependencies
- CPM uses conservative estimates with built-in safety; CCM uses aggressive estimates with pooled buffers
- CPM measures progress against task durations; CCM measures buffer consumption
- CPM starts tasks as early as possible; CCM uses late start scheduling

Exam Tips: Answering Questions on Critical Chain Method

1. Know the terminology
- Understand terms like project buffer, feeding buffer, resource buffer, buffer management, and fever chart

2. Recognize buffer calculations
- Project buffer is typically 50% of the critical chain duration
- Feeding buffers are typically 50% of the feeding chain duration

3. Identify CCM scenarios
- Look for questions involving resource constraints
- Note mentions of safety margins, buffer management, or early finish incentives

4. Understand CCM benefits
- Shorter project durations
- Better handling of uncertainty
- Improved focus on critical activities
- Enhanced visibility of project status

5. Common exam traps
- Confusing critical chain with critical path
- Misunderstanding buffer purpose and placement
- Assuming CCM eliminates all time safety (it pools it instead)
- Missing the resource constraint focus

6. Practice with scenarios
- Try identifying critical chains in networks with resource constraints
- Calculate and place appropriate buffers
- Determine appropriate actions based on buffer consumption rates

Remember that CCM is fundamentally about managing uncertainty and resource constraints simultaneously. Questions will often test your understanding of how CCM addresses these challenges differently from traditional scheduling methods.