Schedule Deviations

Understand the reasons that lead to a lack of schedule adherence and p-factor values being lower than one. 3 min read.

General Principle

The p-factor connects the baseline schedule to project execution, which assumes,

  • Portion of work performed before the ES line
    • Execution in line with the baseline schedule.
  • Portion of work performed after the ES line
    • Execution sensitive to the risk of rework.

Impediments and Work Under Risk to Measure the p-factor

The p-factor is a management tool that detects impediments or constraints during project execution else detects the portion of work performed under risk.

Schedule Deviations

Schedule deviations that lead to a lack of schedule adherence and a p-factor being lower than one include,

  • Baseline estimate deviations: Changes in baseline activity time/cost estimates during project execution might lead to unexpected time/cost performances and shifts in resources.
  • Deviations in EV accrues: The choice of PV accrue needs to made before project start, e.g., % complete, 25/75, 50/50, etc. fixed formulas, and when it differs from EV accrue the p-factor will report inefficiencies.
  • Early or late start times: Similar to the baseline estimate deviations, early, or late activity starts might lead to unexpected project performances and shifts in resources.
  • Activity overlaps: Violating original precedence relations logic and allowing overlaps between activities results in activities being executed with incomplete information (since their predecessors have not finished yet) and might involve a certain degree of risk and a probability for rework.

While it would appear the p-factor is similar to SPI(t) it is fundamentally different as it detects not only impediments during project execution but also the portion of work performed under risk. Situations can exist whereby the SPI(t) value lies close to 1 (denoting perfect performance) with a p-factor value significantly lower than 1.

Schedule Rework

The p-factor assumes that the risk of rework is the result of inefficient use of resources that were shifted from constrained to less constrained activities to gain earned value. Since shifted resources work without the necessary inputs, a portion of the work will be performed under risk. Consequently, this decreases the total earned value resulting in an effective earned value, which assumes a fraction of the work performed under risk will need rework.

Microsoft Project Demonstration

Shown below is a Microsoft Project demonstration project, which is adequately resourced and costed. This project has a schedule duration of 9-weeks and a cost budget of $150. The delivered project and the resulting tracking information, show a final duration of 11-weeks and an actual cost of $210.

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Schedule Rework Results

Shown below is the EV value portions performed under risk,

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Schedule Rework Conclusion

By observing Schedule Adherence Index (SAI) Trends during project progress, the potential value of rework can be identified, and proactive steps can be taken.

A SAI exceeding 0.10 indicates a need to investigate a lack of process discipline, poor planning, poor management else external schedule pressures.

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