- Sometimes known as Critical Path Analysis
- CPA is a project analysis and planning method that allows a project to be completed in the shortest possible time
Information needed for CPA
- A list of all activities required to complete the project
- The time (duration) that each activity will take to completion
- The dependencies between the activities (eg, activity D cannot be completed until both activities B and C are done.)
What is the Critical Path?
- The sequence of a project activities which add up to the longest overall duration. The critical path determines the shortest time possible to complete the project.
Why is the Critical Path so important?
- Any delay of an activity on the critical path directly impacts the planned project completion date (ie, there is no float on the critical path)
EST - Earliest start time LFT - Latest finish time
Calculating ESTs
- The first node will always have an EST of 0
- ESTS are calculated left to right
- Add the duration of the activity to the EST of the previous node
- If more than one activity leads to a node, the highest figure becomes the new EST
Calculating LFTs
- Give the last node of the project an LFT equal to the EST
- Work backwards from right to left
- Subtract the duration of the activity from the LFT
Right to left is lower, left to right is higher
Calculating the float
- The float is the duration an activity can be extended or postponed so that the the project still finished within the minimum time Calculated as:
- LFT less Activity Duration less EST
Identifying the Critical Path
- Activities with a float of 0 cannot be delayed without delaying the entire project
- Such activities represent the “critical path”
Use of critical path analysis
- Estimate and minimise project time
- Support project costing and evaluation
- Plan and organise resources
- Prioritise tasks
- Help provide direction
Advantages
- Reduces risks and costs of complex projects
- Encourages careful assessment of the requirements of each activity in the project
- Help spot which activities have some slack or float and could transfer resources
- A decision-making and planning tool
- Provides managers with a useful overview
- Links well with other aspects of planning
Disadvantages
- Reliability of CPA largely based on accurate estimates and assumptions made
- CPA does not guarantee the success of a project
- Resources may not be as flexible as management hope when calculating network float
- Too many activities may make the network diagram too complicated. Activities themselves might have to be broken down into mini-projects.
