What is Goldratt’s Critical Chain? Estimating Task Time, Common Chain of Events, Critical Chain

What is Goldratt’s Critical Chain?

Eliyahu M. Goldratt has developed many theories for project management. One of the major ones is the theory of critical chain. The critical chain theory measures completing the project on time by adjusting time schedules and reducing the probability of the project getting late. It results in a delay of the project until it reaches the late schedule instead of the early schedule as it is being done in the case of older scheduling methods.

The late schedule arranges all tasks on the critical path, and a buffer is allowed onto the schedule for reaching the completion date. Goldratt suggests that a delay in the project work encourages the project team members to learn from the knowledge gained while doing other assignments or part of the project.

A project schedule consists of two types of tasks, critical and non-critical tasks. The critical chain tasks are the traditional critical path, which means that they do not have any float after the solving of resource conflict. The tasks other than critical chains are non-critical tasks and carry some float with them.

These tasks combine to form groups to be represented as the sub-projects of the main project. Goldratt calls these chains‘ feeder chains’. The feeder chains do not depend on critical chains, however, a task on the critical chain can depend on feeder chains.

A, B, C, and D are the feeder chains where task P, which is on the critical chain, is dependent on them. This shifts all feeder chains to the critical path. The feeder chain tasks will result in a delay in the project schedule. A buffer may be used to avoid this situation.

• Estimating Task Time
  
• Common Chain of Events
  
• Critical Chain

Estimating Task Time

The following measures must be taken into consideration for setting the schedule correctly:

• The critical chain of the project must be computed once resource conflicts and schedule constraints are resolved.
  
  
• The critical path should be buffered. This can be done by calculating a two-standard deviation buffer. Its application may be such that the project starts earlier than its start date or the scheduled date or by promising the stakeholders a later project completion date to the early finish date.
  
  
• Group the feeder chain tasks into feeder chains.
  
  
• Calculate the two standard deviation buffers for the feeder chain. Once done, the scheduling of tasks in the feeder chain must be done as per their late project schedule dates minus the calculated buffer.

After adopting this scheduling method, feeder chains have a 95% probability of being completed within their buffered schedule and not disturbing the critical chain tasks. The critical chain tasks are also buffered so that the probability of missing the buffered promise date of the project completion is 95 percent.

Common Chain of Events

According to Goldratt, tasks discussed in the previous section may lead to the following chain of events:

• If the time taken by activities is already known in advance and their paths are independent of each other, the situation may lead to an underestimation of the actual project time needed for its completion.
  
  
• Project team members tend to inflate the time as compared with the estimated time for activities due to the underestimation of project time.
  
  
• Inflated time leads to work filling for the available time. The workers do not inform the project manager of the early completion of the task. This generates a warning for the team members for the safety time which may be misused by them.
  
  
• The project development and deadlines get missed by the team members.
  
  
• Some of the unknown safety time in turn makes the procedure of assigning priorities to the tasks difficult. The vague assignment of priorities results in poor multitasking.
  
  
• Poor multitasking develops an increment in task durations and leads to irregular demand for resources by the activities of the project such as some activities may demand overloaded resources and others for under-loaded.
  
  
• As there will be more resources, this will force us to carry out more projects to fully utilize all the resources.
  
  
• The addition of more projects will result in reduced multitasking.

According to Goldratt, this chain of events leads to adverse situations. The work gets piled up, team members get pressurised to complete all the work by multitasking. This in turn increases the time taken for completing activities, and thereby, increases the project time. Due to this, the organization will be able to complete fewer projects only.

Critical Chain

The critical chain concept considers some problems that lead to project delays and inefficiencies of tasks. These problems are:

• The time duration for tasks is not known and are independent of each other
  
• The laborers may increase their work time to protect themselves
  
• The completion of tasks early to their scheduled time is difficult
  
• The project will extend to cover the extra time
  
• The tasks may not start until it reaches the last minute
  
• Multitasking may lead to interruption
  
• The demand for resources will not be reasonable
  
• Task delays may happen and finally more projects will come up to balance the resource utilization.

To rectify these problems, some feeder time buffers must be considered every time while planning for the project, specifically for an IT project. The project buffer is added at the end of the project when there is a need for more time and money. The successful completion of projects depends on the availability of bottleneck resources required by the task, and some buffers are considered for the resources which feed those bottleneck resources.