Most projects use deterministic scheduling i.e. single point estimates for time and cost. It is important to consider that in order to achieve reliable credible
project plans, uncertainty must always be taken into consideration. In general projects must adhere to these guidelines when estimating time and cost:
• Estimates must include uncertainty
• Estimates must have a high probability of being met.
• Estimates must reveal the project’s true critical path.
It is important to emphasize that when estimating using deterministic methods, meeting completion dates have 50% chance of being met. Whereas projects
utilizing statistical methods that include uncertainties and confidence levels of 90% are credible and more accurate. The stochastic method assumes that all
possible times for some specific activity might be represented by a statistical distribution. Once again, schedules are now credible and have facts to back up the
estimation process.
