Issue Identification and Appraisal
A subject that raises emotions within our industry is the decision how to deal with schedule updates when out-of-sequence work has been performed. Having spent the past 20 years working for ‘the Client’ our Project Controls procedures stipulated that contractors needed to use ‘retained logic’ when scheduling, during that time it was occasionally noted there were differences in Earned Value reporting. This week’s problem statement is “What is the Impact of Retained Logic and Progress Override to the Earned Value?”
Within Oracle P6 in the schedule options there are three options, ‘Retained Logic’, ‘Progress Override’ and ‘Actual Dates’ see figure 1. We will review all three in this blog along with their effects on earned value calculations.
Figure 1 – P6 Schedule Options
Develop the Outcomes for each
Oracle P6 User Guide mentions the schedule update methods very briefly and does not go into a lot of detail, “When scheduling progressed activities use: Specify the type of logic used to schedule activities that are in progress. When you choose Retained Logic, the remaining duration of a progressed activity is not scheduled until all predecessors are complete. When you choose Progress Override, network logic is ignored and the activity can progress without delay. When you choose Actual Dates, backward and forward passes are scheduled using actual dates.”
- Actual Dates
Using this method, the update method uses the actual dates and the existing logic, so in effect there appears to be no difference to using the retained logic method (refer to figure 2). Further online research confirmed this from an article called ‘Retained Logic and Progress Override in Primavera P6’ where it stated “The remainder of the activity is still treated the same as when we use Retained Logic. P6 will not allow the remainder of the activity to continue until its predecessor is complete.”
Figure 2 – Schedule Update using Actual Dates
- Retained Logic
As the title suggests, this method retains the existing network logic, so an out-of-sequence activity which has a Finish to Start logic tie, the successor will have a gap in the bar until the predecessor finishes (refer to figure 3).
Figure 3 – Schedule Update using Retained Logic
- Progress Override
Progress override ignores the network logic and progresses out-of-sequence activities as if the Finish to Start logic tie did not exist. It does not change anything in the network just ignores the tie and schedules the activities. This results in a lower float calculation than retained logic as the activity is not gapped/pushed out to match completion of the predecessor (refer to figure 4)
Figure 4 – Schedule Update using Progress Override
In effect, there are only two methods to evaluate here as the ‘Actual Dates’ method uses similar methodology to the Retained logic method so this method will be discarded from the rest of the topic.
To evaluate the effect Retained Logic or Progress Override has on the EV calculation, a small resource loaded schedule was developed and an out of sequence activity introduced. The schedule has 25 activities, 7 have been completed leaving 18 remaining. There were no constraints and the schedule log is clean apart from one out-of-sequence activity that was introduced for this evaluation.
Analysis and Comparison of the Alternatives
Before diving headlong into the analysis, it’s probably a good place to briefly mention why out-of-sequence activities occur. These tend to crop up when an activity has been identified that can be started ahead of the sequence it had originally been planned. For example, there are two activities A & B, the original network showed that A had to complete before B started. However, after some analysis it was determined that since A had progressed past a certain point that B could commence before A finished. So, B is started and when a P6 schedule update is performed it recognizes this and flags the out-of-sequence activity as an error on the Schedule Log it produces. This is probably due to the original schedule logic being defective when it was developed. For certain, these need to be fully evaluated prior to implementation so it does not affect the critical path activities.
By rights the error should be addressed and the logic revised and the schedule log free from errors. Remember any logic changes made should be put onto the schedule changes register which the PCM & PM review and sign-off weekly/monthly given the reporting cycles.
For the purposes of this blog, the out-of-sequence activity is still there, and how each method deals with the profiling of costs is what needs to be reviewed.
Progress Override Earned Value Analysis
Figure 4 above showed that the bar was intact with no gaps and the schedule had zero float so was still on track to complete on time. The costs for the activity were distributed from week 6 to 9 (4-week timeframe) and the cost profile is shown on figure 5.
Figure 5 – Cost profile of activity A4020 using Progress Override
Retained Logic Earned Value Analysis
As demonstrated in figure 3 the retained logic method puts a gap in the bar, review of the cost phasing of activity A4020 shows that the costs are distributed from week 6 to 10 (5-week timeframe) see figure 6.
Figure 6 – Cost profile of activity A4020 using Progress Override
To better see what is happening, refer to Table 1 which compares both methods.
Table 1 – Comparison of Progress Override vs Retained Logic
Table 1 shows how the Earned value figures change with two different profiles for the same activity depending on the method chosen. Progress override shows an unimpeded cost profile, while the Retained Logic cost profile includes the delay caused by the effect of predecessor logic.
Table 2 – SWOT analysis of methods
Selection of Preferred Alternative
Based on the analysis, the preferred method for reporting Earned Value should be ‘Progress Override’ for reporting against in-progress activities.
Monitoring Post Evaluation Performance
The issue of using ‘Progress Override’ instead of ‘Retained logic’ is a much larger discussion than just the ‘earned value’ discussion. There is a plethora of arguments out there regarding the use of Progress Override due to the ignoring of network logic. The key to all this is ensuring sufficient detail is provided in the original planning as outlined by the GAO Schedule Assessment Guide Best Practice 1 – capturing all activities. The backup to this is fixing the defective logic that is causing the P6 errors documenting any changes individually on a schedule changes register.
- Primavera P6 Enterprise Project Portfolio Management [Computer program] 15.1.Redwood shores, CA, USA: ORACLE (2016).
- According to Oracle online P6 Professional Help (2017), “When scheduling progressed activities use: Specify the type of logic used to schedule activities that are in progress. When you choose Retained Logic, the remaining duration of a progressed activity is not scheduled until all predecessors are complete. When you choose Progress Override, network logic is ignored and the activity can progress without delay. When you choose Actual Dates, backward and forward passes are scheduled using actual dates.” (No page number)
- According to R.Hendricks, “The remainder of the activity is still treated the same as when we use Retained Logic. P6 will not allow the remainder of the activity to continue until its predecessor is complete.”, retrieved from tepco.us website (August 2015, page 5 figure 1 lower comment note)
- Woolf, M. B. (2012). CPM mechanics: The critical path method of modeling project execution strategy. Rochester, MI: ICS-Publications.
- 3.3.7 Multi-Attribute Decision Making. (2015, November 2). Guild of project controls compendium and reference (CaR) | Project Controls – planning, scheduling, cost management and forensic analysis (Planning Planet). (n.d.). Retrieved from http://www.planningplanet.com/guild/gpccar/managing-change-the-owners-perspective
- 3.3.04 Force Field or SWOT Analysis. (2015, October 3). Guild of project controls compendium and reference (CaR) | Project Controls – planning, scheduling, cost management and forensic analysis (Planning Planet). (n.d.). Retrieved from http://www.planningplanet.com/guild/gpccar/identify-risks-opportunities
- United States. (2015). Best Practice Checklists. In GAO schedule assessment guide: Best practices for project schedules (pp. 25/26). U.S. Government Accountability Office.