In defense of Critical Chain

One of the more subtle changes in the Sixth Edition of the PMBOK Guide is the elimination of all references to Critical Chain Method (CCM).

The rationale for this excision was not provided in Appendix X1 of the Guide which provides details of most of the Sixth Edition changes so I can only speculate that this might have resulted from the desire of the volunteer standards committee to cover commonly used tools and techniques for schedule development, and with the addition of agile release planning perhaps CCM became an easy sacrificial lamb.

Many years ago, I worked in an organization where I attempted to introduce CCM as an approach to managing key resource availability challenges as well as shifting leadership focus from individual tasks to milestones.

Unfortunately, this failed miserably.

A fundamental tenet of the methodology is using optimistic activity durations by stripping out padding and by aggregating uncertainty into buffers at the end of activity sequences. I was unable to convince team members to provide such aggressive estimates given the organization’s prevailing culture. Given that a fair bit of padding remained in each activity duration estimate, the buffers ended up being bloated and milestone dates were later than would have been previously planned.

However, some of the key lessons remained with me which I was able to apply later.

1. Eliminate multitasking of high demand, low supply resources. It’s really tempting to squeeze out every iota of working time from such team members, but the opportunity cost of context switching is much greater than for other team members. So while I encourage the elimination of multitasking for all core team members, if that is unrealistic, at least do it for your “drum” resources.
2. Centralize uncertainty into contingency reserves and defend those reserves. Calling these buffers does not resonate well with senior management as the perception is that these will be consumed carelessly. Position them as contingency reserves and they can start to appreciate the necessity of having some shock absorbers to protect the timelines from known-unknowns.
3. Obsess over milestones and not individual tasks. Estimates are probability distributions – some activities are bound to be late and some will be early. A good project manager keeps their eye on the key milestones and while they are aware of the give and take which results from variation in activity end dates, they won’t micro-manage the team to those. This not only reduces perceptions of micromanagement while empowering individual team members, but it also keeps everyone’s eye on hitting the milestone date. Scrum incorporates this principle by focusing team efforts on sprint goals and commitments and not just on individual tasks.

Use of CCM requires a level of scheduling discipline which is absent on many projects and it does lend itself well to deterministic or predictive projects. But just because you can’t use the method as a whole doesn’t mean it doesn’t contain some good practices which could be applied to your project.