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Critical path in Early & Late dates curve

8 replies [Last post]
Ashb .
User offline. Last seen 18 weeks 2 days ago. Offline
Joined: 25 Nov 2008
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Hi to all

 

In the banana curve of early and late dates where does one can mark or highlight the critical path, runs through the project life cycle.

Please advice

Regards

Shahul Badhusha

Replies

Miklos Hajdu
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Joined: 13 May 2011
Posts: 97
Groups: GPC Malaysia

Steve,

Thanks for your comment

The original question was: In the banana curve of early and late dates where does one can mark or highlight the critical path, runs through the project life cycle.

I wanted to point to the fact that upper S curve is based on the critical activities + the rest of the activities at their earliest time, and the lower S curve is based on the same critical activities + the rest of the activities at their latest times, so the only possible answer to the question is to show show the critical path as I mentioned.l  My opninion that this  has no any practical use.  But again, you cannot "mark or highlight the critical path runs through the project life cycle" from a project S-curve, 'cause all the project S curves incorporates the critial path (and the rest of the activities)!!!

Miklós

Stephen Devaux
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Posts: 655

Hi, Miklos.

In the scenario you describe, the S curve for JUST the 10 planned critical path activities will reach $10M (if you want to just focus your BCWS on the planned CP, which some people do).  The S curve for all 1000 activities will reach $100M on either the Early (ASAP) or Late (ALAP) dates, only by a later route on the Late dates. 

The ALAP BCWS eliminates the float distortion in the SPI, where completing a $1.1M task while it has 200D of float outweighs completing a $1M task on the CP. This sometimes causes PMs to do non-CP work at the expense of CP work, thus maintaining a high SPI while the schedule is actually slipping. Loading the BCWS onto the Late S curve (where there is no float for any activity) attempts to alleviate this problem.

One final note: if tracking to the Late BCWS, one should never allow SPI credit for work done ahead of schedule (i.e., in a reporting period before the ALAP date for the activity).  Thus the ALAP SPI should never be able to rise above 1.0.  But a project with an ASAP SPI of .92 might still be on schedule (if the .08 is all float), whereas an ALAP SPI of .99 means that SOMETHING has slipped beyond its float, and therefore the project is heading for a late completion unless changes are made.

Hope that helps.

Fraternally in project management,

Steve the Bajan 

Miklos Hajdu
User offline. Last seen 8 years 51 weeks ago. Offline
Joined: 13 May 2011
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Shahul,  Guys,

The S-curves based on the activity dates and on the activity costs.

Now imagine a network with 1000 activities and all together $100 million cost.

The critical path consists of ten activities and has $10 million cost. So the S curve for the project will reach $100 million and the S curve for the  critical path will end at $10million at  the project end.

Seems to me that your answer do not reflect for that.  Was it me, who misunderstood the question?

If yes please explain!

Miklós

George Archibald
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Shahul,

Hope this answers ur question as simply as possible :

The top line of the banana curve (S-Curve) is the one that relates to the early start dates and hence the critical path activities (assuming curve is for all activities). This is only true on the planned dates and will not be true once actual progress is recorded.

 

Regards,

George.

Ashb .
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Joined: 25 Nov 2008
Posts: 772

Many thanks to all

 

Regards

Shahul Badhusha

Stephen Devaux
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Joined: 23 Mar 2005
Posts: 655

Daniel Limson wrote:

"However, there maybe other activities with minimal float which can be considered critical."

In general parlance, this is certainly done -- but I would caution against it.  The (actual!) critical path is not just relatively "more critical" than other paths, it's completely different:

  1. None of the other paths add time to the project, but tasks on the CP do (i.e., they have drag).
  2. Time being money, none of the other tasks reduces the project value and/or increases (indirect) cost, but those on the CP do (i.e., they have drag cost).
  3. The true cost for non-CP tasks (even those with only one day of float) is just the cost of their resource use; the "true cost" for CP tasks is the sum of the cost of their resource use plus their drag cost. Thus a good planner will recognize where, by adding resources to a CP task, the true cost of that task will be reduced through reduction in its drag cost.
  4. Insufficiencies of specific resources that are being used on tasks that are not on the CP are not delaying the project completion (and creating drag cost); resource insufficiencies on the CP are delaying the project and should be identified and targeted for increases.

Thus a CP activity is not just relatively different from a non-CP one -- it's qualitatively different.

Also, with regard to Shahul's question about the banana curve, it's important to note that if one is using earned value schedule tracking (schedule performance index), if the earned value is loaded onto the early dates, the SPI will be distorted by float. It is entirely possible to be on schedule (i.e., no task has slipped beyong its float) and have an SPI of .89 or less, if the delays are all off the CP.  For this reason, an ALAP SPI is often a more reliable metric than the standard (ASAP) SPI.  (However, if using the ALAP SPI, it's important to never allow taking of EV credit for work accomplished in a period before it was scheduled.)

 

Fraternally in project management,

Steve the Bajan 

Rafael Davila
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Posts: 5079

Shahul,

Two lines create the Banana Curve, usually based on all activities cost/resources, one for the earlist happening of all activities and another for the latest happening of all activities.

Critical path activities are a sub-set and within critical path, all critical activities ealy and late dates are equal under traditional CPM theory with no constraints. Therefore if none of the activites under critical path are cost/resource loaded and you create the cummulative cost/rosuce curve for critical activities you will get nothing, if loaded you will get something, a single line/curve bellow the Bananana Curve.

Photobucket

Regards,

Rafael

Daniel Limson
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Hi Shahul,

This is the first time i heard that term "banana curve", anyway, the longest path leading to a key date or completion date is always your critical path. However, there maybe other activities with minimal float which can be considered critical.

If your programme is link properly and there are no loose ends or constraints, you can filter the completion milestone activity and go on a backward pass by clicking the driving predecessor until you reach the starting point, the commencement date.

Best regards,

Daniel