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Earned Schedule with P6

5 replies [Last post]
Eliuh Akinpeloye
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House,

I'll like to know if anyone using the P6 has applied the principles of Earned Schedule especciall Spi(t). I will appreciate if I could be guide through please.

 

Thanks

Replies

Rafael Davila
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Joined: 1 Mar 2004
Posts: 5065

Steve,

Drag helps to select the best way for crashing project duration.

Words quoted from a paper by Vladimir Liberzon presented at the Construction CPM Conference 2019.

http://www.spiderproject.com/index.php/publications/139-con-cpm-con-2017

It is interesting the issue is on how it is possible to have different schedules from different software and how floats for same activity can be different. 

It is often possible to employ alternative resource allocations resulting in schedules with identical overall durations but different timings for individual activities; in one schedule an activity may be critical but in another it may have significant float, total float is activity and schedule property.  This “nonexistent” total float in some alternative schedule is often referred to as Phantom Float.  The infamous Phantom Float that has been a challenge when calculating floats in resource constrained schedule for decades. 

We must acknowledge the possibility of the alternate schedule sequences and Phantom Float or we might end up making our decisions using incorrect scheduling information.

Best Regards,

Rafael

Stephen Devaux
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Joined: 23 Mar 2005
Posts: 655

Wow! Rafael, I wish I could have written that as clearly as you did!

Some comments:

"Drag helps to select the best way for crashing project duration.

When in trouble Drag metric helps while EV & ES does not, in any case EV & ES might get you into trouble because potential problems might be masked by compensating positive and negative schedule deviations."

So glad to hear you say that! As I recall, you were initially somewhat skeptical of the value of the drag metric. Over the years, I have hesitated to ask if you feel it has helped you -- so I was delighted to read this by someone whom I regard as a premier project management practitioner!

I still don't understand why, more than 10 years after Spider introduced CPM drag calculation and 5 years after it started computing resource schedule drag (and 3 years after Asta Powerproject started caluclating it in CPM!), Primavera still does neither! I believe that Spider Project (and Vladimir!) will be remembered in history for initiative and leadership in bringing to fruition the full range of critical path metrics.

30 years ago, I worked for a company that marketed a PM s/w product that didn't compute free float, and we often lost sales because of that. So why anyone would either purchase or market a product that does not compute drag is beyond me!

For anyone wondering why drag is so important, here are two articles:

The Drag Efficient: The Missing Quantification of Time on the Critical Path

2016: The Year of the Drag

 

"Earned Value Analysis does not distinguish between the works done on critical activities and activities with sufficient floats. A project could be late but EVA will not notice this problem if Earned Value exceeds Planned Value."

This is right on the money! But it doesn't HAVE to be that way! A small number of simple changes (the most complex is a separate EV baseline for schedule based on the backward pass of the CP algorithm) could make SPI (and SV, and even SPI(t)) much better metrics. The final two chapters in my book Managing Projects as Investments both explore the many problems with EVM and show simple fixes that would greatly improve the methodology.

 

Fraternally in Project Management,

Steve the Bajan

Rafael Davila
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Earned Value Management [EVM] does not distinguish available float, it does not distinguish between critical and non-critical activities. Tracking variance at the activity level without taking into account float makes no sense. We must pay attention to critical activities and resources where EVM is of little or no help.

  • An S-curve is a result of schedule logic. On the level of activities, projects tend to have many paths, some of them critical, other not. A tiny (if compared to total project duration) schedule variance of an activity can become a cause for substantial rearrangements in the project network, it can change critical path or order of activities, enforce a total reorganization of works. This cannot be captured by either Earned Value or Earned Schedule calculations - potential problems might be masked by compensating positive and negative schedule deviations.
  • Earned Value Analysis does not distinguish between the works done on critical activities and activities with sufficient floats. A project could be late but EVA will not notice this problem if Earned Value exceeds Planned Value.
  • Earned Value Analysis motivates project managers to do expensive tasks first delaying cheaper activities that could have higher priorities.
  • The Department of Defense [DOD], the father of the creature is against the use of EVM in fixed price contracts. 
  • Department of Defense Earned Value Management Implementation Guide
  • 2.2.3.7 Exclusions for Firm Fixed Price (FFP) Contract Type. The application of EVM on FFP contracts and agreements is discouraged, regardless of dollar value.

The schedule contract milestones give us all we need to know if ahead/behind schedule; Cost Accounts tell us if we are under/over budget.  It is simple; no esoteric procedures such as EVM are required, no EVM jargon only a few at the field understand. If you must live with EVM learn its limitations.

  • Earned Value Management as a tool for Project Control
  • However, if to be implemented, the method should be used according to its purpose: it is not a tool for forecasting; instead, it facilitates progress monitoring, determination of project status (on time? to budget?), identification of potentially negative occurrences and a rough estimate of their combined effect on the project’s outcome. If the project is to be managed consciously, these occurrences should be then investigated into by means of more accurate methods.

Activity drag is the amount of time that an activity on the critical path is adding to the project duration.  Alternatively, it is the maximum amount of time that one can shorten the activity duration before it is no longer on the critical path or before its duration becomes zero. Drag helps to select the best way for crashing project duration.

When in trouble Drag metric helps while EV & ES does not, in any case EV & ES might get you into trouble because potential problems might be masked by compensating positive and negative schedule deviations.

Stephen Devaux
User offline. Last seen 23 weeks 4 days ago. Offline
Joined: 23 Mar 2005
Posts: 655

Hi, Eliuh and David.

It's nice when a software package provides its users with all the data and metrics they might ever need. And SPI(t) -- and earned schedule in general -- is IMO marginally better than regular SPI. But all SPI calculations have major flaws that not only distort the metric but that invite contractor "gaming" of the metric to look better.

SPi will never be a great metric because earned value is based on cost/resource usage and schedule is always based on something completely unrelated, i.e., the as-built critical path. A couple of simple changes could make EV at least somewhat aware of the CP (such as using a separate baseline for schedule), but it would still leave much to be desired for schedule tracking. And besides, no one seems to either care enough nor understand enough about EVM to implement the simple fixes.

What I really don't understand is why truly important and hugely valuable PM metrics, such as critical path drag, drag cost, and the DIPP aren't included in packages like Primavera which claim to be top tier packages.

Fraternally in project management,

Steve the Bajan

David Kelly
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Eliuh,

Excellent question.  I have supported Primavera products as my profession for about 30 years, and have NEVER had this raised. This is remarkable. What are my clients doing, if they do not measure SPI(t) , and show forecast curves based on it?

This metric is missing in P6.

Doubtless Vladimir or Rafeal will be along in a minute to explain how Spider does it, and the huge Primavera user base will either not understand or not care.

I despair sometimes, I have witnessed astonishing improvements in the technology to support project management in my 40+ years in the job, but there has not been a corresponding improvement in the human resources to exploit that.

I haven't answered your question. It is possible to do but is complex. I have never had to write it down becuase nobody wants it in the Primavera world becuase its not there! I wonder how many P6 users could write down the formula for SPI(t).

Can I ask if your question was to educate yourself, or has a client asked for this?