Critical Chain Project Management

Putting Together a Critical Chain Project Plan

In Part 1 of this series, I looked at the some of the reasons why projects fail to deliver on time. In this article we’ll look at how to use the Critical Chain approach to address these problems.

Most of us, as we’ve seen, will add a safety margin to duration estimates. Then, because of things like Student Syndrome and Parkinson’s Law, we’ll use up this margin when we do the work. The result: the project delivers later than maybe it could have done. Critical Chain attempts to identify these safety margins and strip them out. In this way people will be focused on delivering to a more aggressive target. This minimises the effect of many of the problems we met in Part 1:

Parkinson’s Law – the work now expands to fill a shorter timescale so reducing the effect on our project.
Student Syndrome. Even if people leave their work till the last minute, they’ll be starting earlier than before.
People won’t worry about setting unrealistic managerial expectations of early delivery – as everyone is working to the aggressive timescales
Other parts of the project that are dependent on you will need your work earlier, adding more pressure to work quicker.

The practicalities of stripping out these margins are not easy. How do you identify how much of a margin each person adds? You could reduce all the estimates by a rough rule of thumb say 30%. There are two problems with this; everyone may now simply adapt their behaviour and pad out their figures by a further 30% and each person’s method of calculating their safety margin will be different.

Another approach would be to ask everyone for two figures, one that they are almost 100% likely to achieve and another that is aggressive but achievable. Probably the 100% likely figure will be higher than a padded normal estimate and the aggressive one will be lower. This will only work if people are open and honest. The only way you can achieve this is to stress there will be no detrimental consequences of not hitting the aggressive figures, although everyone must commit to try as hard as possible to achieving them.

Once we’ve identified the aggressive and 100% likely estimates we can start to create our critical chain plan. We assume that 50% of people will be able to hit their aggressive figure and the other 50% will need their margin. We create our plan using the aggressive estimates and then at the end we add another task called the project buffer. The project buffer is the summation of all the safety margins – but as we’re assuming not everyone will need them we’ll multiply this by 50%.

This method is set out in the slide show below. Probably the critical chain plan will give an earlier estimated delivery date than a normally constructed plan. And because we are now focusing people’s attention to finishing to more aggressive targets – in theory we should deliver earlier as well!

Critical Chain Slides Part 2

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The plan we’ve constructed in this article is quite simple. In part 3 we’ll look at what happens when we make things more complicated by having critical and non-critical tasks in our plan.