Activity Duration Estimating by Anticlue

How long is something going to take? It is the ever nebulous question. An Estimate is the calculated approximation of a result. An estimate is based upon input data which may not be well defined. When constructing a schedule, it is common to ask resources how long an activity is anticipated to take. This process is called Activity Duration Estimating.
The inputs for Activity Duration Estimating are:

1. The Activity List – The Activity list identifies work tasks that will be included on the Project Schedule. Remember only activities that are within the scope appear on this list. The Activity List contains all of the tasks for which a duration needs to be projected.
2. Activity attributes – Activity attributes list the assumptions or constraints about timing and location of activities and who will be responsible for them.
3. Project Scope Statement – The Project Scope Statement is a broad view of the project helps project managers estimate the duration of project activities. Project managers use the Project Scope Statement as an input because it includes deliverables, constraints, and assumptions that apply to the overall project. Specific milestones or limitations imposed by the project's customer, including project deadlines and reporting requirements, are described in the Project Scope Statement.
4. Risk Register – The Risk Register describes the effect and probability of events that may delay or disrupt the project. The likelihood of negative events need to be include in the estimate.
5. Activity cost estimates – Activity cost estimates provide approximate quantities of resources allocated to specific activities. If the budgeted cost for an activity limits how many people or how much equipment can be used for a specific activity, this needs to be accounted for in the duration estimate. Also keep in mind the law of diminishing returns. There is a point in time where resource additions, just won’t help to speed up the project.
6. Activity resource requirements – Activity resource requirement detail the number of hours of effort or equipment time needed to complete an activity. The type and quantity of resources needed are part of the calculation of activity duration.
7. The resource calendar – A resource calendar provides availability for people, equipment, and materials needed to do the work activities.
8. Enterprise environmental factors – Enterprise environmental factors capture the external environment in which a project organization operates. Information about the effect of environmental factors may be gathered from commercially available estimating databases or from the organization's own records.
9. Organizational process assets – Organizational Process Assets should have historical information about previous project and standard operating time to complete a request.

As more information is gathered about the activities included in a project, the duration estimates can be refined. There are common tools and techniques to estimate how long an activity will take. These are:

1. Expert judgment - Experienced coworkers or outside advisers can provide expert judgment. They can recommend shortcuts and identify risks that might be overlooked otherwise.
2. Analogous estimating - Companies perform the same activities in one project after another. Analogous estimating bases estimates on the actual duration of earlier activities.
3. Parametric estimating - Project managers estimate the duration of an activity by calculating how long it will take to complete a required quantity of work at a standard rate for one employee or one piece of equipment. For example, if we know that it takes 4 hours to setup a single server. We could expect it will take 2 days to setup 4 servers.
4. A three-point estimate - A three-point estimate adjusts a duration estimate to reflect the probability of both positive and negative events. It's a weighted average of an optimistic or best-case duration, the most likely duration, and a pessimistic or worst-case duration. It is common to use a most likely weight of 4.
   To calculate a three-point estimate of the duration of an activity, do the following:
   • Determine the duration - Determine the duration for the most likely, optimistic, and pessimistic scenarios.
   • Assign weights that reflect the probability each estimate will turn out to be accurate - A weight of 4 is commonly assigned to the most likely estimate likewise the pessimistic and optimistic estimate receive a weight of 1.
   • Multiply each of the estimates by their respective weights - The result is the weighted duration (WD) for that estimate. Total all the weighted durations, and find the sum of the weights.
   • Divide the sum of the weighted durations by the sum of the weights - The result is a three-point duration estimate that reflects risks and opportunities that can affect the activity.
5. Reserve analysis - Reserve analysis creates a buffer in the schedule. Reserve time is added to the estimated duration of an activity in which delays are very likely. Project managers frequently add reserve time by increasing their initial duration estimates by a fixed percentage. For example, it may be well know that any purchase will take 6 weeks to go through the authorization process.

The process of estimating the duration of project activities creates two resulting outputs which are used as the foundation in developing the Project Schedule.

1. Activity duration estimates - The first of the outputs is activity duration estimates. The estimated durations show how much time is required for each activity that will appear on the Project Schedule.
2. Activity attributes – Activity attributes are updated with the assumptions and constraints that are a part of the estimate.

The Activity Duration Estimating process yields an estimate of how long each activity in a project will take to complete.

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