Estimating Activity Duration in Project Management Video

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  • 0:03 Estimating Activity Durations
  • 1:25 Activity on Arrow Diagrams
  • 2:08 Activity on Node Diagrams
  • 3:22 Lesson Summary
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Lesson Transcript
Instructor: Carl Lovell, PMP

Carl has taught grad-level college Project Management and Quality. He holds a Masters degree in Business and is a certified Project Management Professional.

Creating realistic activity duration estimates is critical to producing a meaningful project schedule. In this lesson, you'll learn the importance of realistic activity durations and how to network diagrams to validate your schedule.

Estimating Activity Durations

You have a new project and your team has created a good activity list through brainstorming sessions that you have led. Now you need to estimate the duration of those activities to determine if you can meet the deadline established with the project customer. What do you do?

While you want to be aggressive with the schedule, you know that it will not make the customer happy if you miss the final delivery date. At the same time, if you are too conservative, you don't want to tell the customer that you cannot meet the deadline at all and lose the project.

In an effort to create realistic durations, you start by looking at prior experience on similar projects. You can use the actual completion durations for the same activities that your team performed, or other company teams performed, on similar completed projects. When prior experience is not available, you gather the appropriate team members and brainstorm an estimated activity duration based on their expert judgment. In some cases, industry-provided estimating tools may be available.

Once you have determined an estimated duration for each activity, you'll need to create a network diagram to display the relationship between the activities and calculate an overall duration for your project. In general, there are two approaches to creating network diagrams: activity on arrow (AOA) and activity on node (AON).

Activity on Arrow Diagrams

The activity on arrow (AOA) network diagrams are useful in getting a display of the relationship between activities but are limited in use for analyzing the overall project duration. The activity on arrow approach places the activity and its duration on the line connecting related activities in the project.

The relationships displayed in the network diagram show each activity connected to the activity, or activities, that precede (come before) or succeed (follow). When you get all the relationships displayed correctly with the estimated durations, you can calculate the overall duration of the project, based on following each path through the project. The longest duration path through the network diagram represents the critical path.

Activity on Node Diagrams

The activity on node (AON) network diagram (sometimes called activity in the box) are similar in development to the activity on arrow diagrams except the activity and its associated duration is displayed on the node rather than the arrow. Nodes are the points where arrows intersect.

Because you are placing the activity and the associated duration at the node, typically in a box, you have space in the box to include additional information. As you analyze each path moving forward through the AON diagram, you can add information in each box that indicates the earliest an activity can start and the earliest it will finish. Again the longest path through the network diagram will be the critical path.

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