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CHAPTER 7 PROJECT SCHEDULING AND TRACKING 187

Wilkens [WIL99] notes that “the distinction between the BCWS and the BCWP is that the
former represents the budget of the activities that were planned to be completed and
the latter represents the budget of the activities that actually were completed.” Given
values for BCWS, BAC, and BCWP, important progress indicators can be computed:
Schedule performance index, SPI = BCWP/BCWS
Schedule variance, SV = BCWP – BCWS

SPI is an indication of the efficiency with which the project is utilizing scheduled
resources. An SPI value close to 1.0 indicates efficient execution of the project sched-
ule. SV is simply an absolute indication of variance from the planned schedule.

Percent scheduled for completion = BCWS/BAC
WebRef
provides an indication of the percentage of work that should have been completed
A wide array of earned
value analysis resources by time t.
(comprehensive
bibliography, papers, Percent complete = BCWP/BAC
hotlinks) can be found at provides a quantitative indication of the percent of completeness of the project at a
www.acq.osd.mil/
pm/ given point in time, t.
It is also possible to compute the actual cost of work performed, ACWP. The value
for ACWP is the sum of the effort actually expended on work tasks that have been
completed by a point in time on the project schedule. It is then possible to compute

Cost performance index, CPI = BCWP/ACWP
Cost variance, CV = BCWP – ACWP
A CPI value close to 1.0 provides a strong indication that the project is within its
defined budget. CV is an absolute indication of cost savings (against planned costs)
or shortfall at a particular stage of a project.
Like over-the-horizon radar, earned value analysis illuminates scheduling diffi-
culties before they might otherwise be apparent. This enables the software project
manager to take corrective action before a project crisis develops.

7.9 ERROR TRACKING
Throughout the software process, a project team creates work products (e.g., require-
ments specifications or prototype, design documents, source code). But the team also
creates (and hopefully corrects) errors associated with each work product. If error-
Error tracking allows
you to compare current related measures and resultant metrics are collected over many software projects, a
work with past efforts project manager can use these data as a baseline for comparison against error data
and provides a collected in real time. Error tracking can be used as one means for assessing the sta-
quantitative indication tus of a current project.
of the quality of the In Chapter 4, the concept of defect removal efficiency was discussed. To review
work being conducted.
briefly, the software team performs formal technical reviews (and, later, testing) to
find and correct errors, E, in work products produced during software engineering