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A Critical Look At Critical Chain Project Management


... that are new to project management: choose between CCPM or mainstream methodologies. ... Provide flexible advance notice of upcoming work to critical resources ... – PowerPoint PPT presentation

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Title: A Critical Look At Critical Chain Project Management

A Critical Look At Critical Chain Project
Best Practice Project Management
  • Tzvi Raz, Ph.D., P.M.P.
  • Tel Aviv University, Israel
  • tzvir_at_tauex.tau.ac.il
  • Robert Barnes, M.Sc., Dip. Mgmt, P.M.P.
  • The iE3 Group Ltd, New Zealand
  • robert.barnes_at_xtra.co.nz
  • www.robertb.co.nz
  • My presentation supported by

  • Introduction - What is CCPM?
  • Critical analysis of CCPM
  • based on the evidence in the research literature
    and in practice.
  • CCPM - substitute for or addition to conventional
  • NB - I have significantly edited this
    presentation since the conference

Section 1. Introduction
  • Critical Chain Project Management is -
  • A fresh look at Project Management from Eliyahu
    Goldratt ( Critical Chain)
  • Applies Theory Of Constraints (TOC) to Projects
  • Claimed to achieve dramatic successes for
    projects, as TOC did for processes ( The
  • Intuitively Plausible
  • Seems to hold answers to many of the problems
    that have long troubled Project Managers
  • Creating huge interest in the PM community
  • eg, at least one paper on CCPM in most PM Network

Critical Chain Project Mgmt
  • Is it New and Brilliant?
  • or Largely Hype?
  • First - what is it?
  • (How does it differ from conventional PM?)

An Overview Of CCPM
  • Step 1. Identify Critical Chain
  • Initial Schedule -gt Critical Path. (A-gt B-gt D)
  • Resource leveling -gt Critical Chain. (A-gtB-gt C-gt
  • Critical Chain - The longest path through the
    network after resource leveling.

An Overview Of CCPM (contd.)
  • Step 2. Make hidden buffers explicit.

Hidden Buffer
Unused Hidden Buffer is Wasted!
Why is hidden buffer wasted(1)?
  • Origins in workers conflict -
  • Want to finish tasks on time
  • so need buffers
  • Want to be productive (busy)
  • need plenty of work, no buffers
  • solve by taking on more work

Why is hidden buffer wasted (2)?
Non-critical Jobs
Another Job(Wkr B)
Another Job2(Wkr B)
Job 1(Wkr A)
Job 2(Wkr B)
Job 3(Wkr C)
Job 4(Wkr B)
  • Wkr B knows that (s)hes not needed until day 6,
  • gt Wkr B keeps busy with other work, and is not
    available until day 6
  • gt if Wkr A finishes Job1 early, job 2 cant
    start anyway
  • gt Wkr A knows that finishing early wont help
    the project
  • gt rather than finishing early, Wkr A will use
    spare time on other tasks

Hence the schedule rule -
  • If estimated durations are correct ON AVERAGE
  • Because
  • Schedule gains are lost
  • Schedule losses are passed on in full

CCPM Step 3. Buffer Management
  • Step 3. Show buffers explicitly
  • and pool them

Conventional Project Schedule
Task buffers are hidden
within individual tasks
Job 1
Job 2
Job 3
Job 4
CCPM Schedule
Buffers are pooled,
and made explicit
Project Buffer,
Feeding Buffers - the same principle, but on
non-critical paths
Project Buffer
Date 2
Date 1
Feeding Buffer
If Slack remains, then schedule as late as
Resource Buffers - a Wake up call
Feeding Buffer
Critical Chain
Project Buffer
Alert Wkr A
Alert Wkr B
Resource Buffers
Alert Wkr C
  • Adds neither Time nor Cost to the Project

CCPM Project Management (1)
  • Focus on the Critical Chain
  • Ensure resources give CC tasks priority
  • Eliminate multitasking

CCPM Project Management (2)
Its OK for a task to be late
But not TOO Late
Focus on Buffer Consumption. Should be in
Proportion or better
Multiple Projects under CCPM
  • Resources required to work simultaneously on
    several projects should give priority to the task
    of the one project that is in the greatest risk
    of missing its committed date, as measured by the
    remaining fraction of project buffer.

Section 2. A Critique of CCPM
  • Does CCPM deliver?
  • Anecdotal evidence suggests Yes
  • Closer examination more ambiguous
  • There are several points where CCPM assumptions
    can be challenged

1/ Hidden buffers may not exist
  • CCPM assumes that
  • all task owners pad estimates
  • the actual duration expands to fill the time
  • This is very Plausible,
  • but theres no scientific support
  • Research literature contains contrary evidence
    Hill et al. (2000)
  • Personal experience - mixed. Some incorrigible
  • Does reducing task duration reduce commitment?
  • Personal experience - little effect, but suspect
    that there could be some risk of this
  • Do we still get safety margin on top of buffer?
  • Probably yes.

Parkinsons Law
2/ How big should explicit buffers be?
  • CCPM does not provide any scientific or objective
    basis for determining the buffer size
  • Default 1/3 suggested, based on probability
  • No empirical basis for using this probability
  • CCPM uses statistical assumption of independent
    values (for task duration and buffer) - NOT TRUE
  • Experience
  • Discuss with task owner, get agreement
  • Varies widely
  • Optimists, pessimists - estimating errors dont

3/ CCPM gives incorrect Resource Graph
  • When do you need Worker A?

Gantt Chart
Resource Graph. Not this
But This
4/ What if theres insufficient room for feeding
Conventional Plan - had free float
Date 2
Date 1
Should excess buffer be added to the critical
chain? Correct answer is NO, but what do you do
with it? (CCPM ignores this problem). Indicates
a near-critical path - could easily become the CP.
5/ The Critical Chain
  • How good is the resource-leveled schedule that
    serves as the basis for CCPM ?
  • As good as the algorithm used for its calculation
  • The critical chain may change
  • Feeding buffer exceeds the free slack of the
    feeding chain
  • During project execution the critical chain may
    change as resource availability changes or as
    buffers are used
  • This is true of conventional PM also
  • but CCPM may add complexity

6/ Schedule control
  • CCPM achieves schedule control by monitoring the
    extent of buffer penetration.
  • The remaining-work estimate is also subjected to
    inflation by safety margins.
  • CCPM assigns priority to the task belonging to
    the chain with the highest rate of buffer
  • Ignores other important criteria, such as a
    projects strategic or financial impact.

7/ Multi-Project Management
  • CCPM staggers the projects around the
    constraining resource.
  • At any given point in time there could be several
    constraining resources, each leading to a
    different schedule.
  • The premise that there is a single constraining
    resource comes from the steady state of
    manufacturing and operations environments.
  • Consequently we doubt the applicability of the
    solution obtained with CCPM.

8/ CCPM Focus
  • Project success and project management success
    are not equivalent.
  • Project management success meeting agreed goals
    on time and budget.
  • Project success benefits to customers and
  • Both conventional and CCPM deal with project
    management success rather than project success
  • but CCPM focuses exclusively on ON TIME
  • Focus
  • CCPM meeting schedule goals by dealing with
    schedule uncertainty
  • Conventional both cost and schedule.

9/ CCPM is presented as Alternative
  • CCPM is presented as a revolutionary concept that
    replaces current project management knowledge and
  • It is not properly integrated with the accepted
    body of knowledge and state of the practice.
  • Dilemma to organizations that are new to project
    management choose between CCPM or mainstream

10/ CCPM may have high Adoption Costs
  • Specialized software tool needed
  • CCPM presented as a methodology to be adopted as
    a whole ?massive re-education
  • Culture change may be difficult -
  • Give up ownership of the task duration
  • Rely on common buffers to absorb deviations in
    individual task performance.
  • Replace Due Date by Estimated Completion Date
    Range as represented by feeding and project
  • No multi-tasking.

Section 3. Concluding remarks.
  • CCPM has adapted the concepts of bottlenecks and
    material buffers from TOC for operations
    management, calling them critical chain and
    time buffers in projects.
  • CCPM concepts are not necessarily new
  • But does this matter? In our view, NO. CCPM
    would be worthy of study even it were only a
    packaging of old ideas
  • and theres more to it than that!

The Key Question -
  • Is CCPM as a methodology indeed superior to the
    currently accepted project management
  • Some dramatic successes have been claimed.
  • However, we are not aware of studies comparing
    CCPM with a properly-applied conventional project
    management methodology.
  • We DO NOT believe that CCPM is a better
    alternative to conventional PM.
  • We DO believe that CCPM has good ideas which
    should be included in conventional PM
  • PMBOK should take it more seriously

A Parallel
Good ideas from CCPM (1)
  • Account explicitly for duration uncertainty
  • Focus on Project on time, not Task on time
  • Always consider resource availability
  • What is the shortest realistic plan?
  • Critical Chain is a useful term
  • Focus on the key tasks and resources
  • Reduce or eliminate multitasking
  • Management focus

Good ideas from CCPM (2)
  • Constantly monitor the amount of slack (buffer)
    in your schedule
  • Provide flexible advance notice of upcoming work
    to critical resources

Finally, our suggestions
  • Incorporate those CCPM elements that are
    applicable to your environment within a broader
    project management methodology.
  • Consider the broader context
  • Project success vs. meeting due date
  • Reducing uncertainty vs. buffer management
  • Adopt a comprehensive methodology
  • Consider costs and benefits as well as time

Thank you for Listening
  • Are there any Questions?
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