14 Aug Earned Value Management Applied to Small Projects Basic Model (Part 2)
When a task is recovering (a task is recovering when it was supposed to have finished but it is still being executed) EV is going to progress towards PV and PV is always the same causing the progression of SPI towards 1 (the baseline is extending until the task finishes). The following figure illustrates the idea:
The SPI value is expressed in percentage in the right Y axe.
This example illustrates one of the biggest concerns in EVM since SPI in this cases moves way from the real trend of the schedule and if we want to predict future performance based on the classic SPI the predictions will each time be better since SPI is always approaching 1 (that is perfect schedule performance).
In this case we propose that SPI is calculated using the classical way for all the cases except this one. During the recovery period we want to calculate an “Adjusted SPI” that provides a correct prediction therefore: EDAC=Baseline Duration/Adjustedt SPI
Considering that the SPI for a task that is finished is:SPI=Baseline Duration/Actual Duration
In the case of a recovering task our best estimate for the Actual Duration is EDAC and instead of using Baseline Duration we must use (Actual Date-Baseline Start) so SPI does not maintain the same behaviour of approaching 1. Therefore: SPI=(Actual Date-Baseline Start)/EDAC
Replacing EDAC we get: Adjusted SPI=(Baseline Duration/(Actual Date-Baseline Start))*SPI
The next graph compares the evolution of SPI with adjusted SPI.
With the Adjusted SPI we can now calculate with confidence the future project performance and get a clear view of the status of the project. This approach has the advantage of being very easy to calculate using any of the project management software packages or the simplest spreadsheet.