PERT Technique

PERT or Performance Evaluation Review Technique is used on very large projects, mostly by DOD or NASA in building highly complex items. It's also used in conjunction iwht a GANT chart.
It's a pain in the butt.

but that might not be your what your referring to.

I believe the PERT technique is too seldom used because it requires rigorous planning and coordination discipline on the project manager's part. The prerequisite to PERT analysis is seeking and getting qualified optimistic, pessimistic, and most likely estimates from subject matter experts (SME) for each identified activity in a project. Applying the technique is not difficult, but if you are familiar with the basic PERT keep in mind that it is weighted for the most likely estimate, thus the reason for multiplying that estimate by four among the two other estimates used in the formula. You may re-weight the formula for each activity to factor for more risk (pessimism) or less risk (optimism). Also, when performing the basic PERT calculation, (P+(4M)+0)/6, be sure to also calculate PERT standard deviation, (P-O)/6, and PERT variance, ((P-O)/6)^2. Project managers who become adept in seeking and getting the qualified base estimates required to do PERT analysis benefit by producing more accurate activity duration estimates and a more accurate overall project duration estimate. Also, if the three types of estimates required from SMEs for PERT analysis are thoughtfully produced, and if you then calculate PERT variance at two standard deviations, you may report activity duration estimates and a total project duration estimate to your superiors with 95.46% confidence. This doesn't mean all expectations will be met on the project, but properly controlling a schedule with accurate estimates is more likely to result in less schedule and cost variance, or "turbulance". Be sure to also obtain and document assumptions used by the SMEs who generate base estimates so the PERT estimates you produce are tied to the logic for the base estimates. It is up to project managers to increase their use of the PERT in projects, and they should en masse in order to deliver project schedules with more credible durations.

Actually I doubt your question because planning representations like GANTT can be converted to PERT. When planning is not used arguments are often like
- the project is too small to plan
- planning results in too much overhead (for which we do not want to pay)
- other parties are not able to read a planning (but do not want to confess that they cannot)