In this article on Earned Value Reporting we’ll look at something similar to the To Complete Cost Performance Index – the To Complete Schedule Performance Index, or TCSPI. The To Complete Schedule Performance Index tells us the required schedule performance index that will be needed to meet the schedule.
The book “The Project Management Question and Answer Book” by Michael Newell and Marina Grashina is the source for much of this overview.
What is the to complete schedule performance index?
The to complete schedule performance index, or TCSPI, is similar to the TCCPI except that it calculates a required schedule performance index that will be necessary to meet the project schedule. This measure is rarely used. It is included here for completeness. It has the same problems as the TCCPI and is even more abstract and difficult for people to understand.
The calculation for the TCSPI is done by dividing the work remaining by the remaining schedule.
TCSPI = (BAC – BCWP) / (BAC – BCWS)
It can be seen that as a project’s schedule performance index moves below one, the TCSPI will increase and become greater than one. Although called an “index”, this is not really accurate since all indexes indicate something bad when they fall below one and this index indicates something bad when it is greater than one.
There is a mathematical difficulty with this term as well. If a project is over budget toward the end, it is possible for the BAC and the BCWS to be equal. This produces a division by zero and a point of discontinuity.
Under normal conditions it results in a value that indicates the required performance that the project must have from now until the end of the project.
Example:
Suppose a project is somewhere near 50 percent complete:
BCWS = $100,000
BCWP = $95,000
ACWP = $97,000
BAC = $200,000
SV = BCWP – BCWS
SV = -$5,000
What is the TCSPI?
TCSPI = (BAC – BCWP) / (BAC – BCWS)
TCSPI = (200,000 – 95,000) / (200,000 – 100,000)
TCSPI = 1.05
Notice that if the schedule variance remains the same as the end of the project approaches, the TCSPI increases rapidly. Suppose we have the following when the project is approximately 95 percent complete:
BCWS = $195,000
BCWP = $190,000
ACWP = $192,000
BAC = $200,000
SV = BCWP – BCWS
SV = -$5,000
What is the TCSPI?
TCSPI = (BAC – BCWP) / (BAC – BCWS)
TCSPI = (200,000 – 190,000) / (200,000 – 195,000)
TCSPI = 2.00
As we approach the end of the project, the schedule variance has not changed, but the TCSPI has changed from 1.05 to 2.00. This means that the work that must be accomplished from now to the end of the project must take place at a rate that is twice as fast as was originally planned.