Schedule Risk Analysis With Acumen: Effects of Floats And Lags on Results

Marty Fuentes
| May 25, 2021

This article provides an overview on how varying inputs and parameters affect the date outputs, in particular, the P0, P50, and P100 dates, in the Schedule Risk Analysis (SRA) with software Deltek Acumen Fuse. By understanding how Acumen behaves with respect to varying conditions, schedulers, risk managers, and key stakeholders alike will be guided on providing only realistic input values for the SRA.

In this analysis, the effects of the schedule total floats and lags on SRA results or the P-values (P0, P50, P100) are investigated. Four simple schedules were developed using Primavera P6 to understand how results varied when the same single risk was applied to a critical activity, non-critical activity, and to an activity whose criticality was driven by a lag.

The analysis proves that Acumen considers the total float in the output. Meaning, the total float is “consumed” first before driving the linked successors to their probabilistic dates.

See also:

Different Delay Analysis Techniques

Building Information Modelling: The Future of Project Management

Schedule Risk Analysis With Acumen: Different Activity Status

Risk Mapping, Primavera P6 Schedule Critical Activities (Case 06).

Input

A single risk is assigned to a critical activity (criticality driven by logic).
A single risk is assigned to a non-critical activity with different total float.
A single risk is assigned to a critical activity (criticality driven by lag).
1,000 iterations set in Deltek Acumen Fuse.
All other parameters are set to be the same in each case/project shown in Figure 1 below.

Figure 1. Primavera Schedule with Different Criticalities and Activity Risk Mapping.

Table 1. Risk Mapping to Activities with Varying Criticalities.

Output

Figure 2. Risk Exposure Histogram Generated from Acumen (see tabulated values in Table 2).

Figure 3. Risk Drivers Generated from Acumen (see tabulated values in Table 2).

Analysis

Tabulation of the results of Figures 2 and 3 are shown in Table 2 along with calculations for analysis.

Table 2. Results and Calculations

Due to the risk assigned to a critical activity, the P100 date adds 100 work days to the deterministic date (DT) in C06A. This 100 days is also the max duration set on the risk register for C06B, C06C, and C06D.

The total float in C06B to which the risk was assigned is 150 days. With the max duration input of 100 days, the completion date did not move from its DT value. It seems the risk duration consumed the total float first.

To further prove C06B, C06C has less total float than the risk max duration (50 days vs. 100 days). This resulted to the P100 date shifting 50 working days from the DT. The risk duration does consume the total float first before the probabilistic completion date drifts away from the DT.

In C06D, the risk is assigned to a critical activity. But unlike C06A wherein the criticality is driven by logic, in C06D the criticality is driven by the assigned lag. The results of the schedule analysis for both cases are the same.

Takeaways

When the risk is assigned to a critical activity, regardless whether the criticality is caused by logic or by lag, the P100 date drifts from the deterministic date by the same max duration in the assigned risk.
Acumen considers the total float. It is “consumed” first before driving the succeeding activity to its probabilistic completion date.