Post on 06-Apr-2018
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Estimating Duration
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Estimating Duration
The duration of a project is the elapsed time in
business working days
It does not include weekends, holidays, orother non-working days
Work effort is labor required to complete an
activity
That labor can be consecutive or non-
consecutive hours
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Resource Loading Vs Activity Duration
Resource loading means that number of persons assigned to a task
The duration of an activity is influenced by the amount of resources
scheduled to work on it
We say influenced because there is not necessarily a direct linear
relationship between the amount of resource assigned to an activity andits duration
There are diminishing returns for adding more resources
There is a maximum loading of resources on a task to minimize the
activity duration, and that by adding another resource you will actually
begin to increase the duration You have reached the crashpoint of the activity. The crashpoint is that
point where adding more resources will increase activity duration
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Variation in Activity Duration
Activity duration is a random variable because we cannot know exactly
how long it will take
One of your goals in estimating activity duration is to define the activity to
a level of granularity so that your estimates have a narrow variance
There are several causes of variation in the actual activity duration-
Varying skill levels
Unexpected events
Efficiency of work time
Mistakes and misunderstandings
Common cause variation (the reality is that durations will vary for no reasonother than the statistical variation that arises because the duration is in fact a
random variable )
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Methods of estimating Activity Duration
In consulting practice six techniques are found
to be quite suitable for initial planning
estimates as follows
Similarity to other activities
Historical data
Expert advice
Delphi technique
Three-point technique
Wide-band Delphi technique
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Extrapolating Based on Similarity to
Other Activities
Some of the activities in your WBS may be
similar to activities completed in other
projects
Recollections of those activities and their
duration can be used to estimate the present
activitys duration
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Studying Historical Data
Every good project management methodology
contains a project notebook that records the
estimated and actual activity duration
This historical record can be used on other projects
The recorded data becomes your knowledge base for
estimating activity duration
This technique differs from the previous technique in
that it uses a record, rather than depending onmemory
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Seeking Expert Advice
When the project involves a breakthrough
technology or a technology that is being used
for the first time in the organization, there
may not be any local experience or even
professionals skilled in the technology within
the organization
In these cases, you will have to appeal tooutside authorities
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Applying the Delphi Technique
The Delphi technique can produce good estimates in the absence of expert advice
This is a group technique that extracts and summarizes the knowledge of the
group to arrive at an estimate
After the group is briefed on the project and the nature of the activity, each
individual in the group is asked to make his or her best guess of the activity
duration
The results are tabulated and presented to the group
Those participants whose estimates fall in the outer quartiles are asked to share
the reason for their guess
After listening to the arguments, each group member is asked to guess again
The results are presented as a histogram labeled Second Pass, and again the outer
quartile estimates are defended
A third guess is made, and the histogram plotted is labeled Third Pass
Final adjustments are allowed. The average of the third guess is used as the
groups estimate
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Applying the Three-Point Technique
Activity duration is a random variable
If it were possible to repeat the activity several times under
identical circumstances, duration times would vary
That variation may be tightly grouped around a central value,
or it might be widely dispersed In any given instance of the activity, you would not know at
which extreme the duration would likely fall, but you could
make probabilistic statements about their likelihood in any
case The three-point technique gives us a framework for doing just
that
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Applying the Three-Point Technique
To use the method, you need three estimates of activity duration:
Optimistic Time: It is defined as the shortest duration one has had or might expect to
experience given that everything happens as expected.
Pessimistic Time: It is that duration that would be experienced (or has been
experienced) if everything that could go wrong did go wrong, yet the activity wascompleted.
Most likely Time: It is that time usually experienced
For this method you are calling on the collective memory of professionals
who have worked on similar activities but for which there is no recorded
history
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Applying the Wide-Band Delphi
Technique
The combination of the Delphi and the three-point methods
results in the wide-band Delphi technique
This technique involves a panel, as in the Delphi technique
I
n place of a single estimate, the panel members are asked, ateach iteration, to give their optimistic, pessimistic, and most
likely estimates for the duration of the chosen activity
The results are compiled, and any extreme estimates are
removed
Averages are computed for each of the three estimates, and
the averages are used as the optimistic, pessimistic, and most
likely estimates of activity duration
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Estimation Precision
Early estimates of activity duration will not be as
good as later estimates
Estimates will always be subject to the vagaries of
nature and other unforeseen events We can only hope that we have gained some
knowledge through the project to improve our
estimates
In top-down project planning model, we start outwith roughly right estimates, with the intention of
improving the precision of these estimates later in
the project
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Estimating the Resource Requirements
The importance of resources varies from project to project
The six estimation techniques used earlier can be used to
estimate the resource requirements also, for any project
Types of resources include the following- People
Facilities
Equipment
Money
Materials
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People as Resources
People are the most difficult type of resource
to schedule because we plan the project by
specifying the types of skills we need, when
we need them, and in what amounts
There are a few tools you can use to help you
schedule people
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People as Resources-Skill Matrices
The two matrices are used to assign staff to activities The assignment could be based on activity characteristics such
as risk, business value, criticality, or skill development
This process involves gathering inventory data for two
inventories- An inventory of the demand for skills needed to perform the tasks
associated with specific activities. This is represented as a matrix
whose rows are the activities and whose columns are the skills. These
are both current and long-term needs
An inventory of the current skills among the professional staff. This is represented as a
matrix whose rows identify the staff and whose columns are the skills
The columns of both matrices define the same set of skills. This gives us a way to link the
two matrices and assign staff to activities
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People as Resources-Skill Matrices
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People as Resources-Skill Matrices
Skill Categories-This part of the skill matrix is
developed by looking at each activity that the unit
must perform and describing the skills needed to
perform the activity Skill Levels- Skills must be qualified with a statement
of how much of the skill the person possesses.
Various methods are available, and companies often
develop their own skill-level system
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Resource Breakdown Structure
The Resource Breakdown Structure is used to assist
in not only resource estimation but also cost
estimation
TheR
esource Breakdown Structure is determined bythe job families, which are defined by the human
resource department
That definition is simply put into this hierarchical
framework and used as the basis for identifying thepositions and levels that are needed to staff the
project and from that constructing the staffing
budget
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Resource Breakdown Structure
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Estimating Duration as a Function of
Resource Availability
Three variables influence the duration estimate of an activity, and all ofthem influence each other. They are as follows-
The duration itself
The total amount of work, as in person hours/days, that will be done on theactivity by a resource
The per cent per day of his or her time that the resource can devote toworking on it
Many project management software products today allow you to enterany two of these three variables and calculate the third for you
There is no one right way; its a matter of what works best and is mostconsistent with the way you mentally approach estimating
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Estimating Duration as a Function of
Resource Availability
There are four ways to approach the calculation of
duration, total effort, and per cent/day
Remember that two of them are specified and the
third is calculated
The methods are listed here and described in the
units that follow-
Assign as a total work and constant per cent/day
Assign as a duration and total work effort
Assign as a duration and per cent/day
Assign as a profile
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Assign as a TotalWork and a Constant Per
cent/Day
If we know that the total head down, focused work effort
required to do the activity is 40 hours but that the resource
can devote only 50 per cent of his or her typical day to doing
project activity work, then the resulting duration is going to
be 80 hours, or 10 business days
The formula is simply this-40 hours/0.50 = 80 hours
The duration becomes a calculated value based on the per
cent per day and the work
This method is the one that most software products use as
their default method
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Assign as a Duration and TotalWork
Effort
Alternatively, you could use your or someone elses
experience and estimate the duration based on
history
Then the total work could be averaged over thatduration, yielding the per cent per day value. Using
the same values as above, the formula would look
like this-5 person days/10 days = 0.5
Here again were making the assumption of an eight-
hour day. In this case, the per cent is calculated
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Assign as a Duration and Per cent/Day
The third method is to estimate the duration
as previously described and assign the per
cent per day
This method will calculate the total work
effort. The formula works like this-10 days
0.50 = 5 person days
Of the three methods, this is the least used
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Assign as a Profile
The three duration estimating and resource
assignment methods discussed here all presume that
the resource is going to work at about the same per
cent per day for each day of the activity
There will be cases where the person cannot work at
a constant rate because of other commitments
In such cases, the duration is estimated first and then
the work is assigned at different per cents over the40-hour window
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Estimating Cost
Now after that we have estimated activity duration
and resource requirements, we know the resources
that will be required and the number of hours or
volume of resources needed These are the data we need to establish the cost of
the project. Unit cost data can be applied to the
amount of resource required to estimate cost