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PM Essence
Evolution of Scheduling Methods

M. S. Hiremath, PMP
CPM Technique - The first scheduling technique is Critical Path Method. CPM calculates the completion date of the project, using one-time estimate of tasks. Critical Path is defined as the longest path made up of dependent activities.

Ex:- a house will be completed by a certain date say 1-12-2012.( i.e., no tolerance)

CPM scheduling is also known as deterministic scheduling.

PERT Technique - PERT stands for Program Evaluation Review Technique. It is a probabilistic scheduling technique. Here we use a three time estimate i,e Pessimistic, Most likely and Optimistic for each task of the project, and the longest path i.e. critical path is arrived at. This is the PERT duration of the project. According to statistics, there is only 50% confidence in completing the project in the PERT calculated duration. In the case PERT, we say, a house will be completed by a certain date (say 1 Jan 2013), with a tolerance of say one or two standard deviations. We can say the house will be built by 1 Jan 2013, within a range of +/- ONE standard deviation. We also mention a CONFIDENCE LEVEL associated with this range say, 68% confidence level. If we consider one standard deviation as 15 days, then confidence level of 68% would mean the following, If we make 100 houses using this plan, 68 houses would be built by 1 Jan 2013 within +/- 15 days (i.e. between 17 Dec 2012 & 16 Jan 2013). This sounds more realistic!

CCPM Technique - The latest is the Critical Chain Project Management Method(CCPM), addressing behavioral science of resources involving the following :

1. Law of Parkinson (Work expands to allotted time)
2. Student Syndrome (Team members resorting to last minute rush 'Procrastination is the name of the game')
3. Multi-tasking (Lose-lose situations)

Critical Chain is defined as the longest sequence (Timewise) of dependent activities either of resources or of the path taking into account the availability of resources.It is a resource constrained schedule. In addition to technical dependencies, CCPM considers resource dependencies. It makes use of buffer to protect the project deadline.