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Project Management

Critical Chain Method of Project Management

Projects are made up of a series of processes that all need to be completed to deliver the final product. However, with a project, often much of the detail will be unknown at the outset and so it is necessary to constantly review the details to see what impact these details have on the expected finish date of the project. This is best achieved using a structured project management method.

A structured project management method does not guarantee that you will complete your project on time but without a methodology you are certain to miss deadlines and budget targets. The critical chain method provides a project manager with advance warning of difficulties and clearly identifies any resource issues. The role of a project manager is to find ways to turn uncertain outcomes into certain outcomes. Critical chain analysis helps highlight risks and adopts strategies to reduce these risks.

Before a project is entered into there should always be a feasibility study carried out to consider the potential gains, the capabilities required for success and the risks - both financial and non financial e.g. reputation, market positioning, quality of the project plan itself. Once it has been decided to proceed then the first stage is to review a detailed plan with contributions from all those who will be involved in the project. The initial planning process creates a work breakdown structure (WBS) with estimated time spans and task dependencies. The project manager must collate the WBS and produce a diagram linking all the activities together - this diagram is called a network diagram and forms the basis of a gantt chart (Microsoft project is very useful for this). The network diagram is very similar to a process map. There are many similarities between managing a business using process mapping and running a project using process mapping. Businesses have bottlenecks and the business will only work as fast as the constraining bottleneck. Projects have bottlenecks too and these bottlenecks limit the fastest time that the project can be completed in. Consider the example below - A WBS has been created for a training seminar that needs to be start in 40 days time.

Project Stage Activity Description Immediate Predecessors Time (days)
Preparation A Design Brochure and course   7
Preparation B Identify Teachers   8
Preparation C Prepare detailed course outline   4
Applications D Send out brochures and applications A 17
Applications E Send out teacher applications B 10
Selection F Select teacher C,E 4
Selection G Accept Students D 8
Selection H Select Text for course F 7
Final preparations I Order and receive Texts G,H 11
Final preparations J Prepare room for class G 4

Looking at the WBS, task I takes 11 days, but requires G & H to be completed. G takes 8 days and H takes 7 so G is the critical task here. G depends on D which depends on A - The critical path is thus ADGI (7+17+8+11) = 43 days which is 3 days over the desired project length. Some reassignment of resources will be required to reduce the length of time a task on the critical path takes. Some tasks will have "slack" time. i.e. the gap between the latest start date of a task and the earliest finish date of a task. Resource redistribution will affect the slack time in the other tasks. If slack time reduces to zero then the item is on the critical path. Critical chain methodology incorporates resource deployment into the basic critical path analysis and places buffers at points to reduce the risk of the critical chain lengthening. These buffers will be feeding buffers or resource buffers. The work based structure linkages are clearer on the Gantt chart shown below. There is a difference between the critical chain and the critical path. The Critical Chain of a project is defined as the longest sequence of dependent events that prevents the project plan from being any shorter. This differs from the popular definition of a Critical Path in that the Critical Chain definition, by stipulating dependent events, opens the door to resource dependencies as well as to precedence dependencies.

No matter how good a project schedule is or how well resources perform in the execution of tasks in that schedule, if critical dependencies associated with the project are not included in the description of the effort, they represent considerable risk to delivering project value. Completing a comprehensive review of all dependencies with the those responsible for delivering the WBS will reduce the risks of missing critical dependencies in the planning stage.


Software for Project Management I use Microsoft Project. This software is very powerful and can be used for small projects to complex, enterprise scale projects with real time input on task completion. Currently MS Project does not include all the features for critical chain project management - add ins are available such as CCPM, ProChain or Spherical Angle to make up for this deficiency.

Project management and the Theory of Constraints (TOC) Critical Chain-based project management has received considerable attention in the Project Management community since it was broadly introduced in Eliyahu M. Goldratt’s book, Critical Chain (Goldratt, 1997). The concept of critical chain is born out of TOC as the project length is determined by a few critical tasks just as a production process is determined by a constraint. Pritchard (1997), Risk management, goes on to say "The genesis of Critical Chain in the Theory of Constraints (TOC) has yielded a holistic view of project management that provides effective risk-focused approaches not only to scheduling and control, but also to initial scoping and planning, effective resource behaviors, and minimizing cross-project impacts."

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