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Critical Chain Project Management: History and Value
By William R. Duncan

Are there some good ideas being put forth by the advocates of CCPM? Yes. Are they new and innovative ideas? Not as far as I can tell.

CCPM has its antecedents in something called the Theory of Constraints (TOC). TOC borrows heavily from systems dynamics (developed by Jay Forrester at MIT in the 1950s) and from statistical process control (which dates back to World War II). The two key tenets — think in terms of systems with complex interactions rather than in terms of unidirectional flows, and find and fix the big problems first — are absolutely the right approach, but they are also old news to experienced project managers.

In applying TOC to project management, CCPM follows the same trend — some good ideas presented as new insights. Here are a few of the good ideas:

  • Make sure your schedule reflects resource availability and not just activity dependencies.
  • Don’t let people work on activities that aren’t ready to be worked on.
  • Try to keep resources working on one activity at a time to avoid the overhead of context switching.

Again, those ideas aren’t new — all of them are well-documented in the project management literature.

Presenting old ideas in a new light is a time-honored approach that can be found in everything from ancient religious texts to Reengineering the Corporation. Some proponents of CCPM, however, have advocated for the “goodness” of their approach by depicting current project management practices as “bad.” I think that has the potential for causing some organizations to throw out the baby with the bath water.

For example, one advocate for CCPM argued that scheduling activities on their early start date would divert the attention of the “project manager and team from what must be done.” Just not true. Unless the network logic is improperly defined, scheduling activities to start on their early start date is absolutely the right thing to do — it is actually the result of using the critical chain approach! Under the same set of assumptions (full-time resources, resource-constrained scheduling, 50% probability of timely completion, don’t spend your float if you don’t have to), a critical chain schedule will be identical to a CPM “early start” schedule.

CCPM also asks for full-time commitment of resources. This approach will, in fact, improve an individual’s productivity, so do it whenever you can. Remember, however, that getting part-time resources assigned to your project full-time means that something else (another project, your organization’s day-to-day activities) will suffer. Make sure that these resource decisions are made appropriately. There is no free lunch.

I’ve also read material from several CCPM advocates that seems to confuse the process of mathematical analysis with the creation of a schedule. The former facilitates the latter, but they are not the same. Mathematical analysis (whether critical path or critical chain) is a method for calculating early and late start dates so that the scheduler can decide when to schedule each activity.

So, if you’re having trouble with your projects, CCPM may merit a look-see, but remember that there is little magic in tools and techniques. Traditional project management, properly understood and applied, will be just as effective.

William R. Duncan is the principal of Project Management Partners of Lexington, MA USA. He currently chairs the Board of PMCert, the certification body of the American Society for Advancement of Project Management (asapm). He was the primary author of the original (1996) version of A Guide to the Project Management Body of Knowledge and was one of the founding members of the Global Alliance for Project Performance Standards (GAPPS) which has recently published a framework for performance-based competency standards for project managers.

© 2009 William R. Duncan –

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