The standard approach to project taskl duration estimating is the PMBOK® 3 point estimate. Josh has provided several approaches to the discussion of the issues.The top two issues are:
- The anchoring and adjusting error occur when humans make estimates in the presence of uncertainty.
- Failure to understand the underlying statistical distributions produce unfavorable confidence in the estimates
Stochastic process models of task durations appear in other domains - shop floor scheduling, interval estimates, and constrained resource management - are examples. Bayesian networks are another. These paradigms offer significant improvement in the confidence of the estimates needed for credible schedule and cost estimates for projects in all domains.
The issues with the traditional - and many times naive - approaches include:
- Unrealistic assumptions of probabilistic independence.
- Failure to take into account the "estimating in the presence of uncertainty" described in the anchoring and adjustment research.
- The stochastic nature of all project work, that is ignored in non-statistical estimating processes.
- Failure to assess the probabilistic critical path
It is Time to Move Forward
For a project to be successful it must balance schedule, cost, and the technical performance measures. The influence on these three elements are probabilistic rather than deterministic. The outcomes from these elements and their relationships are a function of these probabilistic distributions.
Because of this, we must move forward in our understanding of the behaviors of the project...
- No more single point estimates.
- No three point estimates without acknowledgment of their limitations.
- No naive definition of the critical path.
- No more ignoring the complexities of schedule and cost.
- No using simple minded process for complex projects
