"Time for Project Completion, Art of Estimation"

Duration tasks estimation is all an art! Do I need a crystal ball to guess the right duration for each activity in order to get the good average for work completion? When a first baseline level 3 must be issued, what major settings must be considered to minimize risks of delay?

Currently, there is “Three different options” to fix duration for activities completion:

-        First option when Owner and Contractor are both will to analyze and integrate the “Time Risk Allowance” to each activity duration [TRA settings detailed in the NEC 3 Contract Format]. So in accordance with contract negotiation terms (GTCC and/ or PTCC) and major Key Milestones, duration’s data’s become accurate. Owner accepts by this way “risks margin” highlighted.

Then from there, you have to monitor only progress of the submitted baseline and follow up the Earned Values (EV). This position allows total acceptance of time completion. There’s no reason to review durations submitted in the schedule until a delay will be noticed. At this stage, the Owner “well-weaponed” will be ready for “Claims war” due to discrepancies.  

-        “The first baseline is drifting due to capacity, productivity …” the submitted schedules are not acceptable and a lack of reliability is noticed. In that case, durations must be reviewed quickly to be re-forecasted again regarding the observed productivity or scope’s changes. Construction teams, both superintendents and supervisors, are asked to contribute and correct durations. Their professional background could be helpful by the bottom-up estimation method to re-adjust tasks durations and reforecast the remaining tasks.

-        The first baseline must be built and your WBS is fixed; you attempt to use models and stochastic formulas to estimate your margins and averages. This case will be developed through some common methods widely shared.

To perform the work, here are some Methods to get an estimated time for activities completion:

-        “PERT - Three points estimation approach” which is related to “Beta distribution”. It is very close to CPM Method (Critical Path). The three  following settings are took into consideration to calculate the Estimated Duration (ED) :

      Optimistic Duration (OD) / Pessimistic Duration (PD) / Most Likely Duration (MLD)

The Beta Law: ED = (OD + 4*MLD + PD) / 6 

-        Ginzburg-Golenko Approach for modeling complex projects concludes that the best way to calculate the ED is to use the formula below, available only in a case of what a gap between PD and ED is not very high. Otherwise the Model couldn’t be used.

Ginzburg-Golenko Model: ED = OD + ((PD - OD) / 3 )

-   Pareto Model: The 80-20 rule can be used to estimate duration’s activities, if we consider that 20% of t  he time reflects “a kind of psychological safety margin” or a “risk buffer”, the remaining time would be the real minimum duration affected to the task. The vice-vers-ça can be used, if you consider that with optimal productivity, you only use 20% of time to perform the work, and the remaining time will cover “meetings, shutdowns, sampling, inspection, …”