Originated from Govern./Research (Navy/Lockheed) Focus on time Optimistic, most likely and pessimistic time Originated from private Industry Focus on cost Crash Time and Crash cost PERT x CPM (both 1950s)
PERT Formulas p.231-232 Optimistic, most likely, and pessimistic time Estimated time of task Estimate Variance of task Estimated time of project Estimated variance of project Z
CPM Based on idea that a project has a Normal Time to complete a job. Normal time is the cheapest. If it takes longer or shorter, it will usually be more expensive. Why ?
To crash a project , PM may need one or more of the below, resulting in great cost • Overtime workers • Use breakthrough equipment • Start a phase of the project (Design, for example) before a pre-requisite phase is completed (Analysis, for example) • Hire consultants.
Which Task to Crash ? • Not a steep slope (big decrease in time with only little increase in cost) • Task that is part of the CP. • Crashing the task will not have a negative colateral result to the rest of the company’s activities or projects (for example, need to stop something else to crash that task).
GERT, different from others because: • Not all immediate predecessor activities must be completed before activity is started • Looping back is permitted. • Percentage probability
Tasks not completed Q: Example of a project where not all tasks need to be completed for the project to be completed ? A2: You research three different possible solutions to cure cancer (three different groups). Once one group solves the problem, other group (tasks) can be disactivated. A1: To decide if you give credit or not to somebody you do three types of credit check. If any two comes through with success, credit is conceived.