PTM Phase 4 – Estimating Activity Durations

Submitted by coleen.yan@edd… on Wed, 07/27/2022 - 13:21

Estimating activity durations provides additional information, or confirmation, for cost estimates that may have been completed already. Understanding and agreeing upon likely activity durations contributes to developing your project schedule.

By the end of this topic, you will understand:

  • The three types of activity duration
  • Commonly used tools and techniques for estimating activity duration
  • Activity duration estimates
  • Program evaluation and review technique charts
  • The relationship between numbers of resources and work efficiency.
Sub Topics

The PMBOK Guide defines activity duration as the time between the start and end of a scheduled activity. Depending on the size of the project, the duration can be measured in days, weeks or months.

The following table details the three types of activity duration:

Duration Type Description
Actual duration
  • This can refer to either:
  • The amount of time between the start of an activity and the actual finish date
  • A date on which a progress report is generated (this may be called the ‘data date’ (DD), ‘as-of date’ or ‘time-now date’) – this is the actual duration from the start of the activity and the progress report date
Original duration (OD)
  • This is the amount of time assigned for an activity at the start.
  • It is used in assessing project progress when the actual duration is compared with the remaining duration.
  • The OD remains the same throughout the project and is not updated.
Remaining duration
  • Accurate project reporting requires documenting the time left for each scheduled activity at reporting points.
  • Remaining duration is calculated in calendar units (days, weeks, etc.) from the date the report is created (DD or as-of date) to the estimated finish date.
  • This information is useful in estimating the human resources needed to complete activities.
Resource

Visit the following links to learn about activity durations and how to estimate them:

There are several tools or techniques used for estimating activity duration, including:

Tool/Technique Description
Expert judgement
  • Estimations are carried out by experts who will be working on the project.
  • This is the most commonly used method.
Analogous estimation
  • Duration data is used from similar successful and existing projects tracking well.
Parametric estimating
  • Historical information and various parameters are analysed to estimate duration.
  • It is similar to analogous estimating but is more precise.
Alternative analysis
  • The number of resources is changed to examine different approaches and decide on the best mix.
Published estimating data
  • Articles, books and journals with proven information about similar projects are used for research.
Vendor bid analysis
  • Bids or offers for the work provide estimates for project durations and costs.
  • This is used when external vendors or contractors will be part of the team.
PERT Method
  • Program evaluation and review technique (PERT) calculates the time required to finish a project. See section 5.4. for more information about PERT.

As with other activity estimations discussed in this Learner Guide, you should, as project manager, seek input from people with experience in the work to be done as well as relevant experts.

Tips for estimating activity durations:

women on serious meeting
  • Decide how accurate your estimate should be. More time will be spent on estimating if the project has to be estimated in detail. A less accurate estimate produced more quickly may be all that is necessary to be effective.
  • Include contingency hours to reflect risk or uncertainty associated with any estimates.
Resource

Read about activity duration estimates at the following link:

‘Understanding Estimate Activity Durations in Project Management’ from Invensis

You can record duration estimates for use as a reference by using a template for activity duration estimates to create a table. This will provide input for developing the key deliverable from this phase: a PERT chart.

Resource

The following link includes for your use template for documenting activity duration estimates:

‘Activity Duration Estimates Template’ from My PM

The key deliverable from PTM Phase 4 is a program evaluation and review technique (PERT) chart. This is similar to a network diagram discussed in section 3.4.

PERT charts are used to plan tasks within a project — making it easier to schedule and coordinate team members. …

PERT is similar to critical path in that they are both used to visualize the timeline and the work that must be done for a project. However, with PERT, you create three different time estimates for the project:

The shortest possible amount of time each [activity or] task will take
The most probable amount of time
The longest time tasks might take if things don't go as planned.

Wrike

This is a three-point estimate, similar to the method for estimating resources discussed in section 4.3. PERT is calculated backwards from a fixed end date for projects where contractor deadlines cannot be moved.

Developing a PERT Chart

A PERT chart plots the numbered tasks or events needed to complete a project on a timeline. The tasks are placed as nodes, which are linked by arrows. Task information in a PERT chart includes duration times and the critical path for the work.

A diagram depicting PERT Chart

Durations are an important input for developing the project schedule and can also be included in the project’s milestones. As project manager, you are responsible for these estimates, with input from key project team members or relevant experts.

Although there is a direct link between the amount of work needed and the time it may take, there is no direct relationship between the amount or number of resources assigned to an activity and its duration. However, adding more resources can be effective in shortening duration. This is called ‘crashing the activity’. This is effective only up to a certain point, called the ‘crash point’, where adding more resources increases the duration by decreasing efficiency and risks inconsistent work quality.

As project manager, you may need to consider the optimum loading, or most efficient number, of resources on a task.

Activity 5A: Estimating activity durations for FF

Case Study

Families First Relocation Project – Part 5

The Families First (FF) director has approved your linear responsibility chart and project budget. You explain that next, you will estimate durations for the relocation activities and confirm key dates for the project.

Read the case study ‘Families First Relocation Project – Part 5’. Then, prepare a PERT chart in a separate document or on a piece of paper for review and approval by the FF director.

Activity 5B: Estimating activity durations for your project

In a separate document or on a piece of paper, prepare a PERT chart and confirm the critical path activities for your project from previous Learning Activities.

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