Critical chain project management is based on methods and algorithms derived from constraint theory. The concept of CCPM was introduced in 1997 in Eliyahu M. Goldratt's book "Critical Chains.". The application of CCPM is considered to achieve 10% to 50% of projects faster and/or cheaper than traditional methods developed in the 1910s-1950s (i.e. CPM, PERT, Gantt, etc.).
According to a study of traditional project management methods by The Standing Group and other companies up to 1998, only 44 percent of projects are typically completed on time. Projects are typically completed at 222 per cent of the original plan, 189 per cent of the original budget cost, 70 per cent of the projects do not reach the planned scope (delivery of technical content) and 30 per cent are cancelled before completion. CCPM tries to improve performance relative to these traditional statistics.
detailwith traditional project management methods, 30% of time and resource losses are often consumed by wasteful techniques such as poor multitasking (especially task switching), student syndrome, parkinson's law, built-in delays, and lack of prioritization.
in a project plan, critical chains are sequences of priority and resource-related tasks that prevent a project from completing in a shorter period of time given a limited number of resources. if resources are always available in unlimited quantities, the key chain of a project is the same as its critical path approach.
critical chains are an alternative to critical path analysis. the main characteristics that distinguish critical chains and critical paths are:
1. use (often implicit) resource dependencies. implicit means that they are not included in the project network, but must be identified by looking at resource requirements.
2) lack of search for the best solution - a "good enough" solution is enough because:
as we know, there is no analytical method for finding absolute optimal values (i.e., with a population shortest critical chain).
b. the inherent uncertainty of the estimate is much greater than the difference between the best and the approximate best ("good enough" solution).
3. identify and insert buffers:
a. project buffer
b. connection buffering
c. resource buffering (companies are often reluctant to provide more resources)
4. monitor project progress and health by monitoring the consumption rate of the buffer instead of the performance of individual tasks planned.
The plans to aggregate a lot of safe time added to tasks in the project into a buffer zone — to protect performance on expiration dates and avoid wasting that security time through poor multitasking, student syndrome, parkinson's law, and low-level synchronization integration.
critical chain project management uses buffer management rather than earned value management to evaluate project performance. some project managers find earned value management techniques misleading because it does not distinguish between progress in project constraints (i.e., critical chains) and non-constrained (i.e., other paths). the event chain method determines the size of the project, feed, and resource buffers.
planning
project plans or work breakdown structures (wbs) are created in much the same way as critical paths. the plan starts backwards from the finish date, and each task starts as late as possible.
assign a duration to each task. some software implementations add a second duration: one is the "best guess", or 50% probability duration, and the second "safe" duration, which should have a higher probability of completion (possibly 90% or 95%, depending on the amount of risk that the organization can accept). other software implementations go through a duration estimate for each task and remove a fixed percentage to aggregate into the buffer.
resources are assigned to each task, and resources are scheduled using aggressive durations. the longest resource-level task sequence from project start to finish is then identified as the critical chain. the rationale for using the 50% estimate is that half of the tasks will be completed ahead of schedule and half will be completed later, so the difference in the course of the project should be zero.
because of parkinson's law, student syndrome, or other reasons, ccpm recognizes that tasks are more likely to take more time than shorter, so ccpm uses "buffers" to monitor project progress and financial performance. the "extra" duration for each task on the critical chain – the difference between the "safe" duration and the 50% duration – is collected in a buffer at the end of the project. in the same way, buffers are collected at the end of each task sequence that will enter the critical chain. the date at the end of the project buffer is provided to external stakeholders as a delivery date. finally, establish a baseline and achieve financial monitoring of the project.
the alternate duration estimation method uses monte carlo simulations using probability-based duration quantification. in 1999, a researcher applied simulations to assess the impact of risks associated with each component of a project's work breakdown structure on project duration, cost, and performance. using monte carlo simulations, project managers can apply different probabilities to various risk factors that affect project components. the probability of occurrence can vary between 0% and 100% of the chance of occurrence. enter the impact of the risk into the simulation model along with the probability of occurrence. the number of iterations of the monte carlo simulation depends on the tolerance level of the error and provides a density plot that illustrates the overall probability of risk to the project outcome.
execute
when the plan is complete and the project is ready to start, the project network is fixed and the size of the buffers is "locked" (that is, their planned duration may not change during the project) because they are used to monitor project progress and financial performance.
without slackening the duration of a single task, encourage the resource to focus on the task at hand to complete it and hand it over to the next person or group. the goal here is to eliminate poor multitasking. this is done by providing priority information to all resources. literature and relay competition analogy. encourage each element in the project to move as fast as possible: when they run the "side roads" of the project, they should focus on completing the assigned tasks as quickly as possible, while minimizing distractions and multitasking. in some case studies, actual batons have reportedly been hung by people's tables while they are dealing with critical chain tasks so that others know not to interrupt. the goal here is to overcome the tendency to delay work or do extra work when there seems to be time. the ccpm literature contrasts this with "traditional" project management that monitors the start and finish dates of tasks. regardless of the date, ccpm encourages people to move as quickly as possible.
since the task duration has been planned for a 50% probability duration, there is pressure on resources to complete critical chain tasks as quickly as possible, overcoming student syndrome and parkinson's law.
monitor
according to proponents, surveillance is, to some extent, the biggest advantage of the critical chain approach. since the duration of individual tasks differs from the 50% estimate, it makes no sense to try to force each task to be "completed on time." estimates will never be perfect. instead, we monitor the buffers created during the planning phase. you can create and publish fever charts or similar charts to show buffer consumption as a project completion feature. if the buffer consumption rate is low, the project will reach the target. if the consumption rate may have little or no buffer at the end of the project, then corrective action or recovery plan must be put in place to recover the loss. these alternative plans are required when the buffer consumption rate exceeds a certain threshold (roughly: the rate at which all buffers may be expected to be consumed before the end of the project, resulting in a delay in completion)
wield why consider human factors and work habits
all project work is carried out through people. without considering the human factor, the goal is difficult to achieve. that is to say, successful project management or improving the performance of the project needs to consider some internal factors of people, as well as people's work habits, some of people's natural attributes or nature, and at the same time adopt some innovative management thinking methods to carry out project management. this new method, on the one hand, should take into account the human factor, and on the other hand, it should also consider the convenience of management and easy tracking.
the cause of the delay in the project duration
1. student syndrome
in the student era, it is often encountered that the teacher assigns an assignment in the classroom, such as submitting a learning report, usually a week to complete the report, but often the student requires two weeks to turn in the homework, that is to say, in the time estimation will usually increase a hidden margin, or safety margin. it was supposed to be a week's work, but the student asked the teacher for permission to complete the assignment in two weeks. what would happen if the teacher agreed to the student's request and promised the student to submit the report in two weeks?
in most cases, students may choose to start writing this report at the beginning of the second week. that is to say, in the first week, he arranged his free time to do other work, and from the second week he began to write. there may be some students who did not carry out their work in time after the first week of time passed, but delayed for another day, two days, or even three days, so that his report could not be completed on schedule, even if it was completed on schedule by overtime, it seriously affected the quality of the report.
assuming that the completion of this report takes 5 days, if the work is not started until wednesday of the second week, then the whole work will be delayed. we call this condition student syndrome.
some people bring this habit to work again. statistics show that student syndrome is widely reflected in many projects and many jobs. so here's a parkinson's law.
2. Parkinson's Law
Work expands to fit the allotted time.
that is to say, if the work allows it to delay and postpone its completion, often the work is always postponed to the day when it can be completed at the latest, and it is rarely completed in advance. in most cases, it's projects that are delayed, work that is delayed, or that the task is barely on schedule.
3. analysis of the reasons for project postponement
in addition to the role of student syndrome, it is also because in the ordinary work, those who complete the work early are not only not rewarded, but also punished.
why is it that the work done early is not rewarded but punished?
imagine if your boss gave you a job and planned it to be completed in 10 days, and if you finished it in a week, how would your boss react? he would think that maybe the job wouldn't have taken 10 days in the first place, and it would be natural for you to do it in a week. so you won't get praise from your boss for getting the job done ahead of time. if you schedule the same task a second time, the project plan will be shortened from the original 10 days to 7 days, which means that the result of completing the task ahead of time is to increase the difficulty of the next task.
a similar situation exists in the sale of products, or in the quantity of products processed and produced by workers, with the consequence that the quota for work and sales performance is always increased monthly or annually. as a result, some salespeople have the potential to make sales bigger and sell more products, but they will not choose this practice, but they will have reservations. because he is worried that if his sales break through a new high, it is likely to lead to a higher performance as the basic level of assessment, because of this worry, everyone will have a certain reservation for work, there is a certain safety margin or hidden safety margin.
under such conditions, combined with student syndrome, there is rarely a phenomenon of early completion of projects or early completion of work, and most of them are project delays and delays. this was a fundamental cause of project delays.
4. how to improve the management of the project
so, how to improve the management of the project according to the characteristics of people, according to parkinson's law, according to the work habits and characteristics of student syndrome? the critical chain method is a solution to the above situation.
the difference between the critical chain method and the critical path method is that the critical path method is that the work arrangement starts as early as possible, as early as possible. the key chain method is to delay as much as possible.
proposed considerations the key chain method is mainly based on two considerations:
(1) if a work begins as early as possible and there is often a certain amount of relaxation, time fluctuation and safety margin, the work is often postponed until the last day it permits. during this period, the entire work did not give full play to its efficiency, resulting in a waste of manpower and material resources. if the arrangement is started at the latest, there is no floating and safety margin, which invisibly puts pressure on the staff working on the project, and he has no choice but to try as hard as possible to complete the set task on time. this is an idea adopted by the key chain method.
(2) when making project estimates, it is necessary to try to eliminate some hidden margins in personal estimates. experience has shown that when people make estimates, they tend to estimate according to the time required to be able to 100%. in this case, if there is a 50 per cent chance that only a task will be completed and a 50 per cent chance that the task will be postponed, the original estimate of the time spent on the job will be greatly shortened.
according to the law of average, all the tasks in the project are estimated according to the 50% probability of the project time, the result is that the overall estimation time of the project is compressed by 50%, if it is compressed, as a unified security backup, as a public resource for project management, unified scheduling, unified use, so that the standby resources are effectively used to the place where it is really needed, so that the original project duration can be greatly shortened.
advantage can improve the performance of the project
in order to ensure that the project can be completed, we also need to arrange a margin in the work, that is, to tap the potential in the estimation. if each work is reduced by 50%, the surplus time is arranged according to 50% of the project duration, and the work margin is still arranged according to the latest start of the project, according to the time required for the completion of the project, the last work of the project is first arranged, and then the second work, long-term work, and finally the starting work of the project is arranged. arrange the safety margin at the end of the project duration.
using the backward method of sorting, if there is a delay in the resource in the previous work, the delay in time occurs, which will be reflected in the final time margin. for example, the first phase of development is estimated to take 10 weeks, the actual use of 15 weeks, the increase of 5 weeks, these 5 weeks is actually the time delayed backwards, just the time allowed in the later backup.
it is easy to grasp the key points in project management
the second benefit is to grasp the key points in the management of the project and manage the key work, rather than the need for comprehensive coverage as in traditional project management, and to regularly record the progress of each work, analyze deviations and track the progress of the project. with the critical chain method, only need to pay attention to those projects and work that have been postponed, and if the work is carried out within the normal range, it can be placed in a slightly secondary position in the management work. at the same time, the standby management of the project is carried out, and the overall progress of the project is managed and controlled as a whole. this is a basic principle of the critical chain method.
complete projects ahead of schedule
one of the benefits of critical chain management is the early completion of projects. it is usually at least 1/3 of the time ahead of the critical path method.
as in the example just given, if it is managed according to the critical path method, it may take 45 weeks, and if two work additions are considered, such as 5 weeks of development delay and 5 weeks of copy writing, the total project can be completed within 35 weeks.
the main idea of the key chain method is how to take people's work habits into account in the management work, and adopt a new method to improve project performance according to local conditions in project estimation and project management.
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