Probabilistic project scheduling uses an understanding of the variation in project tasks and the project environment (project risks) to make a quantitative prediction of a range of project outcomes. Instead of providing a fixed date to answer a question such as “When is first oil?” probabilistic scheduling provides a range of answers of the type, “There is a 50% chance of achieving first oil by date x or sooner, and a 90% chance of achieving it by date y or sooner.”
A more general application of probabilistic planning also considers the range of project costs and returns. This evaluation focused on the range of outcomes for key project dates, such as first oil. Quantifying the range and probability of outcomes can aid project planning and decision-making.
Probabilistic scheduling provides a method to quantify the risk management process. Quantifying the impact of potential risks improves decision-making affecting the control of those risks, and potentially on the overall financial viability of the project. It specifically aids the upfront recognition of critical issues and proactive management of those issues.
So how does better planning result in shorter project lead times?
First of all, there are fewer surprises. Having done a proper job of evaluating project risk and task durations, you’re prepared to deal with the “murphys” that always occur during project execution. Since you’ve already prepared, you can respond much quicker, without wasting time.
Second, a good project plan moves these potential risk events off the critical path (if possible!). By moving risk events off the path that determines project delivery, eliminating disruption to your deliveries. That doesn’t happen without planning.
Third, the tasks themselves are stripped of the safety that most project plans have, with all task safety aggregated at the end of the critical chain. Saftey aggregation allows you to manage the safety as a project level item, rather than letting it be dispersed to every resource in your project. That means that you need less, and the overall project duration is shorter with greater certainty of completion on time.
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