Abstract
Earned value metrics are well known measures for assessing the schedule performance of projects. In response to deficiencies from using activity costs in traditional earned value metrics for evaluating a project’s schedule performance, earned duration management was proposed as an alternative measurement approach. In particular, earned duration management gives a new measure of a project’s schedule performance, called the Duration Performance Index, which purports to show how well the project is doing in achieving its target completion date. Herein, this paper demonstrates that, because of the confounding impact of parallel activities in a project, the Duration Performance Index can yield false positives and false negatives about a project’s schedule status. And it shows that claims made about the Index are at best guaranteed to be true for an arbitrarily small window of time. The paper concludes with the observation that earned value metrics for assessing a project’s schedule performance all suffer from the same confounding impact of parallel activities, as well as other issues; and that research on other approaches is needed.
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Notes
Khamooshi and Golafshani (2014) also introduce a metric called duration variance for which they make a similar claim: namely, that duration variance “measures the deviation from the plan on the critical path.” Like Khamooshi and Golafshani (2014), we focus on the Duration Performance Index. However, we show that the two metrics are mathematically equivalent and, therefore, have equivalent behavior.
While the sum of activity durations is measured in time (e.g., days), it should not be confused with calendar time. To avoid this confusion, we use the term “progress” instead of “duration” for such sums.
Analogous to Schedule Variance in EVM and ESM, Khamooshi and Golafshani (2014) define the concept duration variance, DV(t), as DV(t) = ED(t) – t. It directly follows from the definitions that DV(t) is equivalent to DPI(t) in that: DV(t) = t(DPI(t) – 1).
These results are also true in ESM under appropriate assumptions. In particular, if planned value is continuous and strictly increasing over [0, BPD] and if earned value is continuous over [0, APD] and strictly increasing over [BPD, APD] when APD > BPD, then the results for Earned Schedule follow by similar reasoning.
Given that DV(t) = t(DPI(t) – 1), it is obvious that DV(t) is < 0 iff DPI(t) < 1 and DV(t) is > 0 iff DPI(t) > 1. Thus, the issues noted above the Duration Performance Index equivalently apply to duration variance.
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Wendell, R.E., Lowe, T.J. & Gordon, M.M. Dangers in using earned duration and other earned value metrics to measure a project’s schedule performance. Cent Eur J Oper Res 31, 665–680 (2023). https://doi.org/10.1007/s10100-022-00830-4
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DOI: https://doi.org/10.1007/s10100-022-00830-4