CPI and SPI calculation

[John V]

I am having a problem with the calculation of CPI and SPI,
looks like it may be a bug. Problem occurs in the
following scenario;

An activity has a Baseline Start of Dec 1, 03 and Baseline
Finish of Dec 5, 03. Work starts early on this activity
(Actual Start = Sep 2) and the status date is set to Sep
19, 03. In this scenario CPI and SPI are not calculated
(i.e. ACWP and BCWS are not calculated, but BCWP is)
unless the status date goes beyond the Baseline Start date
(i.e. later than Dec 1, 03).

I must keep the original baseline as this was the original
plan and always need to measure performance against it.
But, I must also get an accurate reading for CPI and SPI
and since it will only show up in December, I have to wait
2 months and may be hit with a surprise to my overall CPI
and SPI values. To get around this problem I have tried
saving Baseline1, which shows the activity starting on
Sept 2 and have changed the Earned Value calculation to
use Baseline1. Problem is that this does not help as ACWP
and BCWP are only calculated once the status date goes
beyond the original Baseline Start date and not Baseline1
Start as should be expected. So it appears that using the
new Baseline1 does not help in the calculation.

Am I missing something or is this a bug?

Thanks,

John

 

[Ed Kilner]

I think you are. There is a fiction that the baseline can't change. Sure it
can. You should keep a log to show what you did and you do need a valid
reason.

One reason is pretty good: you changed your plan to start early. Therefore,
your final plan has a BCWS curve different from an earlier plan that you
discarded. Why would you want to measure anything against a plan you
discarded? If you did, how would it show you anything useful about your
performance? Would it not just confuse? Sure would confuse me.

Same thing applies when new scope is added. You need to add a baseline for
the new tasks, because you now have a BCWS different from a plan you are no
longer following. But the baseline log will explain.

Some companies "convert" planning packages to Work Packages in the month
before the work package is going to be performed. The BCWS will be affected
by this "rolling wave" but performance can be related to your real plan.

--
Ed Kilner, P.Eng., PMP

(e-mail address removed) (416) 822-4835

Project Solutions Unlimited www.psu.ca