Estimating Duration

8/2/2019 Estimating Duration

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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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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

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Estimating Duration