Purpose
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.
Definition
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.
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.
SPI Value
|
Analysis
|
Equal to 1
|
A favorable condition; the team is getting work done as expected.
|
More than 1
|
A favorable condition; the team is getting more work done than expected.
|
1 < CPI <= 0.95
|
An unfavorable condition; the team is getting less work done than expected. It is still in an
acceptable condition, but the performance should be improved.
|
0.95 < CPI <= 0.9
|
An unfavorable condition; the team is getting much less work done than expected. It shows the
ineffective project performance and must be improved.
|
Less than 0.9
|
An unfavorable condition; the team is getting an unacceptable less work done than expected. It shows
the deficient project performance. The team should assign the highest priority in improving the project
performance.
|
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
|
|
Frequency and reporting
Planned Value estimates are provided at the beginning of each iteration. Earned Values are reported at the end of each
iteration. The Plan versus Earned schedule chart is reviewed with the team during each iteration retrospective and
discussed with stakeholders to help identify trends.
Collection and reporting tools
Schedule data is collected in IBM® Rational® Team Concert®. IBM® Rational® Insight® reports on this metric at the
executive level.
|