Overview
The Schedule Performance Index (SPI) measures how effectively you are using time in an iteration or in a project. This
helps you see the trend of how are you are progressing compared to the plan. You can use SPI for iteration plans or
project plans. SPI helps the team to understand the efficiency of spending time and they can adjust future plans
based on the trends recorded in previous SPIs.
Measurement Method
SPI = Earned Value / Planned Value
-
Earned Value = Value of completed work items to date in terms of the budget assigned to the
work item. This can be the number of earned velocity (hours, days, ideal days, points) to date.
-
Planned Value = Planned value of completed work items to date. This can be planned velocity
(hours, days, ideal days, points) to date.
Measurement Analysis
SPI indicates how efficiently the project team is spending the time against the plan. SPI should be as close
to one as possible. If SPI is more than one, it indicates a favorable condition, which shows that the team is
getting more work done than they expected according to the plan. If the SPI is lower than one, it indicates an
unfavorable condition, thus the opposite result.
In the following table, by the end of week 4 (9/26/2008), the teams planned to complete 48 hours of work, but they
completed only 36 hours of work. Therefore, the SPI to date of this project is 0.75 (36/48). This indicates that
for each eight-hour working day, they are doing only six hours of the work that they had planned to do,
which means that they are accomplishing only 75% of the planned work each day, on average.
Dates
|
Plan Value
(person-hours)
|
Earned Value
(person-hours)
|
09/05/2008
|
6
|
6
|
09/12/2008
|
20
|
20
|
09/19/2008
|
32
|
32
|
09/26/2008
|
48
|
36
|
10/3/2008
|
87
|
|
|