Time is a key factor on which the success of any project depends. Time constraints are the most critical, and completing a project on time is a challenge. At the initial stage, it is important to correctly determine the subject area and scope of the project. In order not to make adjustments to the calendar schedule in the future and avoid problems in the implementation process.
To cope with time constraints, project management uses various methods, one of which is the PERT estimation method. Before understanding what it is, what are its features, advantages and disadvantages, the article discusses the concepts of the calendar schedule and project time management, as well as the term "critical path".
Schedule and five time management processes
To complete the project on time and achieve an effective result, the project timeline must be professionally managed. If the time is delayed, the negative consequences are budget overruns and insufficiently high quality of work. The main tool for project time managementis a schedule that is sequentially developed through five interconnected processes:
- The scope of work and methods of production are determined.
- The sequence of actions and their relationship is established.
- The duration of each work and the total duration are estimated.
- A calendar schedule is being developed.
- Managing schedule changes.
There are key events in the project, without the occurrence of which further continuation is not possible. Such events are called milestones. The project is subject to variances during execution, and the task of managing deadlines is to reduce their number and size. To do this, you need to control:
- milestone deadlines;
- value indicators of achievement;
- compliance of the achieved results with the planned ones.
In typical projects, the experience of previously implemented programs is used to determine the timing and sequence of work. But due to the fact that each new one is unique, the accumulated knowledge is partially applied.
Types of schedules
Calendar plans are divided into three types: basic, executable, actual. The baseline is a formally approved schedule against which performance and actual data received during the project implementation are subsequently compared. The executable plan contains a complete list of activities with characteristics and relationships and is a network Gantt chart. The actual plan representsis a schedule that changes and is supplemented as the project progresses and information about the actual progress of the work becomes available.
If actual performance starts to deviate from the baseline, a prompt decision is made to take corrective action.
Project critical path
In a project, work is performed sequentially or in parallel. In sequential production, the start and finish dates of some depend on the schedule of others. There are four types of job dependency:
- "finish-start" - the completion of one job depends on the start of another;
- "start-finish" - the beginning of one action depends on the end of another;
- "start-start" - the start of one job depends on the start of another;
- "finish-finish" - the end of one activity depends on the end of another.
When executed in parallel, these actions are independent of each other and are executed at any time.
The critical path defines the longest sequence of activities that ultimately will not affect the completion date of the entire project. It indicates critical works, from the beginning and end of which the final deadline depends. In case of deviation from the schedule, the analysis of the work of the critical path is carried out with subsequent adjustment. The following methods are used for this:
- re-estimate the duration of work;
- additional detail of work;
- search for alternative ways to implement the project;
- paralleldoing work;
- resource increase;
- organizing overtime.
PERT - project evaluation and analysis
In large, complex and long-term research projects, it is difficult to set deadlines and develop a detailed schedule. For them, the PERT method is intended, which stands for the project evaluation and analysis method and is used when the exact duration of the work is unknown.
What are the differences between methods
There are differences between the two methods of project analysis:
- The critical path focuses on the duration of work, and the PERT method focuses on key events (milestones).
- The critical path is used when there is an accurate estimate of the project time, and PERT is used for programs where it is problematic to predict the duration.
- In the critical path method, jobs have any type of dependency, and the PERT method is used for one - "finish-start".
According to the PERT method, project management is the control over the total duration in the presence of uncertainty in the execution of work. To apply it and calculate the duration of the work, three estimates are used:
- Probable Estimate - A period of time when there is a high probability of completion of work.
- Optimistic - the shortest time for which the production process is completed.
- The pessimistic estimate is the longest time it will take towork.
The calculation formula for PERT analysis is as follows: work time=(shortest time + 4 x likely time + longest time) / 6
Advantages and disadvantages
The table below discusses the advantages and disadvantages of using the PERT method:
The method is useful when the project is new and there is little information about the timing of the implementation of such action plans.
Human factors, subjective analysis and estimation inaccuracy may affect the schedule.
The method simplifies planning and reduces project uncertainty.
Updating and maintaining the schedule requires a lot of time and money.
The method gives the exact completion date of the project.
Difficult to manage, there is no guarantee that the schedule will remain the same throughout the project.
The priority task of time management is understanding whether it is necessary to intervene in the progress of the project in order to return time constraints to the basic framework. For a quick analysis of the time indicators of the program, it is important to develop a detailed, convenient and detailed calendar scheme. In the case of large-scale projects, when it is difficult to determine the exact timing of the work, using the PERT method, you can develop the optimal schedule and calculate the most probable deadlinesimplementation of the action plan.