The Critical Chain Method (CCM) is a project management technique that improves performance. It addresses resource constraints and recognizes that people often overestimate task durations. Developed by Dr. Eliyahu Goldratt, CCM evolves from the Critical Path Method (CPM) and incorporates the Theory of Constraints to manage projects more effectively.
Table of contents
What is the Critical Chain?
The critical chain is the longest-duration path through a project, considering both task dependencies (precedence) and resource constraints.
Unlike CPM, which focuses solely on task precedence, the critical chain method accounts for resource contention, which often extends project duration. By optimizing task sequences and resource allocations, CCM aims to deliver projects on time with efficient resource use.
An Insurance Analogy
Imagine fire insurance for five homes.
- CPM Approach: Each home self-insures, assuming it will suffer a serious problem. This approach may not provide enough coverage for a severe issue.
- CCM Approach: Assume not every home will have a serious problem. Pooling contingency resources can cover serious problems and potentially more.
Problems with CPM
- Buffer Overkill: Individual estimates often include excessive buffer times, leading to inefficiency.
- Unproductive Tracking: Focusing on individual task due dates rather than overall project health encourages protectionism and avoidance.
- Individual vs. Team Ownership: Emphasis on individual commitments rather than team ownership of the project.
Differences with Critical Chain
- Reorganized Risk: CCM uses safety buffers to manage risk effectively.
- Buffer Utilization: Focuses on how buffers are used to indicate project health.
- Start Dates: Prioritizes accurate start dates and exploits early finishes.
- Aggressive Completion: Emphasizes aggressive, targeted task completion.
Project Success with Critical Chain
Delivering on time (or sooner) with the expected amount of resources defines project success. Meeting deadlines without exceeding the allocated resources is crucial. Achieving these goals ensures a successful project outcome.
By identifying necessary tasks and their sequences, CCM optimizes concurrent activities, leaving an optimized timeline. Resource constraints are accounted for, ensuring the project timeline is realistic and achievable.
Task Duration and Buffers
CCM estimates task durations based on active time, removing unnecessary padding. Buffers are added at strategic points:
- Project Buffers: Added at the end of the project to absorb risks and uncertainties.
- Feeding Buffers: Added at points where non-critical tasks feed into the critical chain.
- Resource Buffers: Alerts indicating the need for resources before they are required.
Key Phenomena Addressed by CCM
- Parkinson’s Law: Work expands to fill the available time.
- Student Syndrome: People start working intensively only when deadlines are near.
- Murphy’s Law: Anything that can go wrong will go wrong.
- Bad Multitasking: Inefficient multitasking delays the start of successor tasks.
Project Buffers
CCM introduces buffers to manage uncertainties:
- Project Buffers: Placed at the end of the critical chain to absorb delays.
- Feeding Buffers: Inserted at the junctions where non-critical paths join the critical chain.
- Resource Buffers: Alerts indicating when a resource will be needed soon.
Steps in Critical Chain Scheduling
- Identify Activities: Start by defining all project tasks and dependencies.
- Estimate Task Durations: Use 50% confidence intervals (P50) for task durations, assuming focused work without interruptions.
- Assign Resources: Allocate resources and resolve any conflicts.
- Identify the Critical Chain: Find the longest path considering both task dependencies and resource constraints.
- Add Buffers: Insert project and feeding buffers to account for uncertainties and finalize the schedule.
Implementation Example
Consider a project with tasks A, B, C, and D:
- Remove Safety Time: Reduce task durations by 50%. If Task A originally takes 6 days, reduce it to 3 days.
- Create Schedule: Schedule tasks based on late finish dates and resource availability.
- Add Buffers: Add a project buffer of 50% of the task durations at the end of the project. Add feeding buffers for non-critical tasks.
Advantages of CCM
- Reduced Project Duration: Eliminate unnecessary buffers and multitasking to significantly reduce project duration. This approach streamlines processes and enhances efficiency. Consequently, project timelines become shorter and more manageable.
- Effective Resource Utilization: Resources are allocated more efficiently, avoiding delays and maximizing productivity.
- Focus on Critical and Non-Critical Tasks: Ensures efficient completion of all tasks. Prioritizes critical tasks while also addressing non-critical ones.
Implementation of CCM
Organizations like the US Navy, Lucent, NASA, the US Air Force, and Philips have successfully implemented CCM. It improves project performance by addressing common project management issues. These issues include unproductive multitasking, late completions, and budget overruns.
Critical Path Vs Critical Chain Method
| Basis | Critical Path Method (CPM) | Critical Chain Method (CCM) |
| Primary Focus | Task Dependencies | Resource Constraints and Task Dependencies |
| Project Schedule Basis | Critical Path | Critical Chain |
| Risk Management | Individual Task Padding | Project and Feeding Buffers |
| Task Scheduling | Early Start Dates | Late Start with Resource Leveling |
| Task Duration Estimates | Padded, Conservative | Aggressive, Realistic |
| Buffers | No Buffers, contingency built into tasks | Project Buffers and Feeding Buffers |
| Resource Management | Assumes resources are available as needed | Considers resource availability and constraints |
| Execution Focus | Individual task performance against the schedule | Encourages early task completion, reduces multitasking |
| Estimation Approach | Single conservative estimate per task | Aggressive estimates with buffers for safety |
| Monitoring | Tracking task progress on critical path | Monitoring buffer consumption and task progress on critical chain |
| Control | Monitoring buffer consumption and task progress on the critical chain | Ensuring critical chain tasks start ASAP and monitoring buffer usage |
Final Words
The Critical Chain Method offers a robust approach to project management by addressing resource constraints and improving task estimates. CCM ensures projects timely completion of projects and within budget by focusing on buffer utilization and resource availability. This technique is valuable for any project manager aiming for efficiency and success.
