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My schedule shows an overall variance value of -1%. Does that mean schedule slippage or the opposite?

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It depends on the math. Typically you take actual complete minus planned complete. If negative, then you're behind schedule.

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Regular monitoring of the project status allows for the computation of the project performance variance, which is the difference between actual performance and the baseline schedule. When considering project management, there is no a single variance, and my understanding from what you have written is that you are referring to the schedule variance. The schedule variance (SV) as the schedule performance index (SPI) are both used to measure time performance in monetary unit. The difference between the value of the work completed (EV) at the current time (AT) and the value of the work planned (PV) at that time is measured by both measures in a different way. As SV is computed as the difference EV-PV, it can be clearly negative. In this case the project is behind schedule. When the difference is zero the project is on schedule, while when the different is positive the is project ahead of schedule. The SPI is computed as the ratio between EV and PV, so it is a positive quantity. When SPI<1, the project is behind schedule. On the other hand an SPI>1 indicates that a project is ahead of schedule, while an SPI=1 means that the project is on schedule. However we have to be careful. As a matter of fact, EV reports the value of the work completed at a particular time, whereas the PV reports the planned value at that same time. Thus EV represents the ideal planned timing for the present value earned because it is expressed as a percentage of the planned value and does not necessarily relate to actual expenditures. As a result, the discrepancy between earned value and planned value at the actual time displays the project's timeliness. To be more precise the behavior of SV (and SPI) is unreliable as we approach the end of the project. This is because of the computation of EV. In fact, EV is equal to PC* BAC, where BAC is the Budget At Completion. The percentage of project completion (PC) varies between 0% (at the project start) and 100% (at the end) and hence EV varies between 0 and BAC exactly as the PV curve. Thus, SV will be always equal to zero at the project end, and this regardless of the project delay.

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  • Earned Schedule solves for this problem as it relates the gap between AT and Earned Schedule, which is on the x-axis, instead of Earned Value, which is on the y-axis. It's validity does not degrade like SV does. Jun 5, 2023 at 12:08

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