Estimating Activity Duration
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Inputs
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Activity list
 Work task in scope for the project
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Activity attributes
 Describe requirements or limitations
 Assumptions or constraints about timing and location of activities
 Responsible parties
o
Project scope statement
 Deliverables
 Constraints
 Assumptions
 Milestones or limitations
 Project deadlines and requirements
o
Risk register
 Effect and probability of events that may disrupt or delay the project
o
Activity cost estimates
o
Activity resource requirements
 Number of hours of worker effort to complete an activity
 Type and quantity of resources required
o
Resource calendar
 Which people, equipment and materials can be assigned for each work
activity
o
Enterprise environmental factors
 External environment in which the project operates
 Government regulation
 Material limitations
o
Organization process assets
 Practices for conducting work
 Data from earlier, similar projects
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Tools & Techniques
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o
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Expert judgment
Analogous estimating
Parametric estimating
 How long it will take to complete a required quantity of work at a
standard rate for one employee for one piece of equipment
o
Three-point estimates
 Adjusts estimates to reflect the probability of both positive and
negative events
 Weighted average of optimistic, most likely and pessimistic duration
 Typically the weight of the most likely scenario is 4, optimistic and
pessimistic or each 1
 Apply the weight to each duration and sum the weighted durations
then divide by the sum of the weights
o
Reserve analysis
 Creates a buffer in a schedule
 Increase schedule by a fixed percentage
Every project includes a series of related work activities. Before you can create
an accurate project schedule, you must create reliable estimates of the amount
of time each activity will take to complete. For any given activity, there are
several techniques you may use to estimate its duration. Select several work
activities from an upcoming project. Use each of the techniques described below
to estimate the duration of each one. Keep a careful record of the duration
estimates that result from each technique and compare them with one another.
When the work activity has been completed, review your records to learn why
some techniques were more accurate than others.
1) Analogous duration:
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Refer to project files for previous projects. How long did a similar work activity
take in another project?
Compare the amount of work performed in the previous project to the amount of
work planned for a similar activity in the upcoming project. Did the similar work
activity in the previous project produce more output? The similar activity in the
upcoming project may take less time because it produces less output. Adjust your
estimate accordingly. Did the similar work activity in the previous project
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produce less output? The similar activity in the upcoming project may take
longer. Increase your duration estimate if you think that's appropriate.
Compare the quantity of resources available for the similar work activities in the
two projects. Were more people or pieces of equipment available in the previous
project? If so, you may need to increase your duration estimate. Are more people
or pieces of equipment available for the upcoming project? You may be able to
reduce your duration estimate.
Compare the types of resources available. Was the work activity in the previous
project performed by more reliable people or equipment? If so, increase your
duration estimate to allow more time for less reliable resources to perform the
work. Will the work in the upcoming project be performed by more reliable
resources? You may be able to reduce your duration estimate.
2) Parametric estimating:
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Determine the amount of work output that must be produced during a work
activity. How many units of output must be created by the activity?
Estimate the rate at which the output will be produced by a single worker or piece
of equipment. State the rate in number of units produced in a given amount of
time, such as an hour, a day, or the entire duration of the activity.
Determine the number of workers or pieces of equipment that are available for the
work activity.
Multiply the number of available workers or pieces of equipment by the estimated
rate for each one to determine the total rate of output. Divide the total units of
output the activity must produce by the total rate of output. The result is a
quantitatively based duration estimate.
3) Three-point estimate:
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Determine the most likely duration for the work activity using either of the two
methods shown above.
Refer to the project's Risk Register or use your own judgment to determine what
events may delay the completion of the work activity. If foreseeable negative
events occur, how will the duration of the work activity change? Determine a
pessimistic estimate for the duration of the work activity.
What events could occur that would allow the work activity to finish in less time
than expected? Determine an optimistic duration estimate for the work activity.
Assign a weight to each estimate that reflects its probability of occurring.
Calculate a weighted average of the three estimates.
4) Expert judgment:
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Show your estimates to a coworker with more experience participating in other
projects with similar work activities. Ask for his or her expert opinion. Which
estimates seem wrong?
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Ask for a thorough explanation of why any estimate seems incorrect. Make
adjustments if you think they're needed.
Outputs
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Activity duration estimates
Activity attributes
o When, where or how activities must be performed
Developing the Project Schedule
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Inputs - Broadview
o Project Scope Statement
 Describes product or service
 Describes assumptions or constraints
 Deadline, milestones and reporting requirements
o
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Risk Register
 Assessment of events that may delay or halt a schedule
 Allow for probability of negative events
Inputs – Specific
o Network Diagram
 Shows how project activities are related
 Allows for proper sequencing
o
Activity Attributes
 How activities will be performed
 Who will perform activities
 Helps to categorize activities
o
Activity Duration Estimates
 Helps determine begin and end of each activity
 Summarized, can help estimate total length of a project
Inputs – Final
o Resource Requirements
 Type and quantity of resources needed
 When resources are required
o
Activity List
 Listing of all activities that comprise the project
o
Resource Calendars
 Identify when resources are available
 Illustrates when resources are available or committed elsewhere
o
Organizational Process Assets
 Overtime
 Work off
 Training
 All other policy issues
Coordinating activities
 Reduces wasted time
Specific Tools & Techniques
 Schedule Network Analysis
 Critical Path Method
 Calculate the earliest finish and start times for activities
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Schedule Compression
What-if Analysis
Resource Leveling
Critical Chain Method
Project Management Software
Applying Calendars
Adjusting Leads and Lags
Schedule Model