I agree; SPI is BCWP/BCWS both of which are measures of $$$. Use of
Physical%Complete is the best way to use this type of data.
There is a lot of discussion (not just in this forum, but all the project
management areas), about measurement of %Complete in its various forms. The
use of SPI compares planned costs against what was earned in a baseline.
Using your HFH house as an example, after building "x" houses the HFH folks
should have a very good idea of what it costs for a foundation, framing, etc.
and those can be estimated in $$$ as part of their overall budget.
Given HFH has established a budget of $x for framing, if it is agreed that
progress will be tracked against these financial indicators (that is the
definition of EV), then no matter what the ACWP or duration is for "Framing"
we cannot earn more than $x in value. It's perfectly reasonable to use the
SPI criteria. If someone decides it will take another 3 weeks (and more
money) to finish "Framing" we still cannot earn more than the baselined value
of "Framing." It does come back to "Time is Money" ... the weighted value of
$ in the BCWS are weighted against time ... there may be very expensive
carpenters loaded up front in large numbers that then trails off to less
expensive framers once the basics are stood up.
I think what we are getting to, and the industry seems to be going in this
direction, is the concept of Earned Schedule, sometimes called "Schedule
Adherence." SPI is a "vertical" measure of completeness on a $ vs time
graph. Unfortunately, SPI closes to 1.0 which is crazy for a task the
finshes late. Instead, many agencies are now adopting "Earned Schedule"
which would be a horizontal measure between BCWP and where (in time) does
this BCWP value appear on the BCWS curve. So we have a measure in time
saying "I am 3 weeks behind schedule." This is the projection of BCWP on to
the BCWS curve and can be interpolated using Excel or some other tool.
It all centers around what the customer and contractor agree are the
measures of success and the weighted contribution of those items to the total
value of "Success". Some posters here seem to vehemently disagree with me,
because we have different fundamental assumptions of what 100% Complete
really means.
For example, suppose we decided to measure success by the pound for the HFH
house. In that case, we weigh all the materials and that becomes 100%. We
then measure the weight (in pounds) of each installed item and take our
%Complete (Physical%Complete to be more correct) against the total weight of
the house. Similar measures would be "work" or $. It would be unfair to say
time was an acceptable measure of success becuase this implies the passage of
time creates value which it does not -- there is no success being created on
a rain day or waiting for inspection.
The discussion of "Where I should be %Complete compared to where I actually
am" depends entirely on how success is measured, and it is not "duration."
Here are a couple of links for additional information.
https://acc.dau.mil/evm
http://www.earnedschedule.com/Docs/Connecting EV to the Schedule.pdf
http://www.earnedschedule.com/Docs/Earned Schedule Leads to Improved Forecasting v1.pdf
http://www.stsc.hill.af.mil/crosstalk/2005/06/0506Lipke.html
http://www.pmforum.org/library/papers/2007/PDFs/Van_De_Velde-10-07.pdf
Hopefully our readers will enjoy...
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Jim
Visit
http://project.mvps.org/ for FAQs and more information
about Microsoft Project
John said:
Jim Aksel said:
To properly status the schedule, first establish a [Status Date]under
Project/Project Information.... Verify all tasks with [Start]<[Status Date]
have a %Complete > 0. Also, for all tasks with [Finish]<[Status Date] they
should be 100%, if they are not 100% complete, extend the task to the right
of the [Status Date]. Move tasks with 0% Complete to the right of the [Status
Date]. There also can be no tasks with [Actual Start] or [Actual Finish]
greater than the [Status Date]. This is proper schedule preparation.
If you have properly costed resources assigned to your schedule, a status
date, and a baseline, then you should insert the Schedule Performance Index
[SPI] column. The [SPI] measures what you have actually accomplished divided
by what you scheduled to accomplish as your baseline -- a measure of 1.00
would be on schedule. SPI>1 ahead, SPI<1 behind. Explore Earned Value in
the help for more information.
Another choice, insert the [Status] column. [Status] will tell you if the
task is "complete", "future task", "late", "on schedule." Please note
[status] considers ahead of schedule to be "on schedule"
A formula can be applied to calculate the %Complete where you should be as
of the status date. The formula must address times when [Status] is (1) Prior
to [Start], (2)during the duration of a task, and, (3) after [Finish]. The
following formula can be applied to a spare column such as [Text1]:
str(IIf([Status Date]<[Start],"0",IIf([Status
Date]>[Finish],"1",ProjDateDiff([Start],[Status Date])/[Duration]))*100)+"%"
The formula can be used to compare with the %Complete field which is also a
duration based calculation.
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If this post was helpful, please consider rating it.
Jim
Visit
http://project.mvps.org/ for FAQs and more information
about Microsoft Project
Jim,
I'll just point out that even though SPI has been embraced for years as
a classical earned value metric, it does NOT measure schedule
performance. Why, because SPI is cost based and contrary to common held
beliefs, time is not always money. My prime example, a schedule to build
a Habitat for Humanity house.
If the use of SPI is suggested for schedule performance, I submit that a
caveat be included that the SPI metric is cost based, not schedule based.
John
Project MVP
