Gantt Chart with risk scenarios

Posted on jueves, septiembre 09, 2010 by Pedro Wave

I will not talk about the economic risk scenarios, because politicians and managers are for this, but we should be aware that, for a project to be successful, it must define its objectives with measurable and SMART criteria:
  • S: Specific
  • M: Measurable
  • A: Accurate
  • R: Realistic
  • T: Time bound
For the Technical Project Management it is used one or more of the following techniques for stimating time:
  • Experts's estimation: Trial based on their experience.
  • Similar estimation (Top-Down): Comparison with similar projects already completed.
  • Parametric estimation: workload * productivity.
  • Three points estimation: Media of the pessimistic, optimistic and realistic values.
  • Simulated estimation: Simulation using software tools.
In any estimate we must be able to measure the potential risk of failure to complete assignments on time, through a range of error. If we do not have previous experience on similar projects or we don't have measures of productivity, the estimation should be done according to the optimistic, realistic and pessimistic scenarios set by the project leader, always advised by his team collaborators.

All planning must have a risk plan and, to make it, a Gantt Chart could be a great help with three possible scenarios: Optimistic, Realistic and Pessimistic, including a different start date for each of these scenarios, according to the Critical Path Method, and that the starting date of each task depends on the date of completion of all its predecessor tasks.

With this program you can do a simulation exercise to measure the three possible scenarios for a project, with various estimates of onset and duration of tasks, to study its evolution over time and likely end dates. Monte Carlo is the most common technique of simulation. The bars of the Gantt charts are used to show the temporal overlapping of tasks.

The Project Management Plan should contain the document Time-scale Base, with the initial planning of the project times, to be compared with the actual project schedule.

I do not like to calculate the time estimation (TE) of each task with the formula:
TE = (O + 4M + P) / 6
shown in this example of Wikipedia, where:
O: The optimistic estimated time,
M: The normal or more frequent estimated time,
P: The pessimistic estimated time.

It is best to get three possible scenarios: best, planned and worst to improve them and to approach the target dates of the project.

In the next Excel sheet I have tried to capture this for an example of Gantt Chart that demonstrates the project management in real time, on any of the scenarios that are presented in order to assist in making decisions that serve to meet the targets set for the project.


The file is written for Excel 2007-2010 and includes Languages sheet that lets you add more languages for internationalization, as well as Spanish and English by selecting the cell B1.

I explain in the next video how to modify the tasks of the Gantt Chart:

If you are interested, Jon Peltier has published an Easier Gantt Chart for Repeated Tasks here.

I hope your comments and suggestions, and the results of your checks, that will help me improve the Gantt Chart, which I thank you in advance.

Traducción al español aquí.

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