Program or Project Evaluation and Review Technique (PERT) assist in planning a certain project. It defines the activities, which should be involved in the process of completing the project and determines the time needed in order to complete these activities. PERT is a useful tool for planning big and complex projects. It concentrates on the different tasks and the way they should be handled by illustrating their sequence and the connection between them in the PERT chart. This technique also allows determining different time periods, which can be used for completing a project; from the minimum to the maximum one. Activities in the PERT chart strictly depend on the previous tasks, which must be finished in order to move forward with the project. It shows exactly when one activity ends and another one begins, and what activities can be performed simultaneously. PERT allows calculating a ‘critical path’. It shows the minimum time required to complete the project, which cannot be prolonged because it will cause a delay of the completion of the entire project.
One of the biggest disadvantages of PERT is that it is used before any details of the project are known. Since the projects, which PERT is designed for, are unique and do not have a fixed set of activities, it is extremely difficult to predict the process of its performance. For example, it does not indicate a precise time required for completing a certain activity. Days or weeks stated in the chart can be estimated by the people, who have never dealt with these kinds of activities and do not know an exact time period needed to complete them. Therefore, these estimates are not reliable and can lead to the errors in the entire project.
Since PERT tasks’ duration is usually underestimated, this difficulty can be overcome by calculating time, which includes the risk of the activity’s completion being delayed. The consequences of underestimation are much more risky than of overestimation. In addition, the duration of the same or similar activities can be checked in other projects, which were previously performed. In case some tasks are going to be performed externally, dates can be checked with the people or organizations, which will be responsible for them. They will be able to give more precise estimations of the completion dates, since they have experience in this matter and will be more accurate that those people, who work with a chart. For example, if the project is to build a house different activities will be performed by professionals. Firstly, architectures must work on the design of the building.
Therefore, they should be contacted in order to negotiate all the details and to estimate the time required to perform the task. The duration then is calculated together with them and is entered to the PERT chart. The duration for the following tasks can be estimated in the same manner.

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