pert estimating

PERT History• The Program Evaluation and Review Technique commonly

abbreviated PERT is a model for project management invented by Booz Allen Hamilton, Inc. under contract to the United States Department of Defense's US Navy Special Projects Office in 1958 as part of the Polaris mobile submarine-launched ballistic missile project. This project was a direct response to the Sputnik crisis.

• PERT is basically a method to analyze the tasks involved in completing a given project, especially the time needed to complete each task, and identifying the minimum time needed to complete the total project.

• PERT was developed in the 1950’s, primarily to simplify the planning and scheduling of large and complex projects. It was able to incorporate uncertainty by making it possible to schedule a project not knowing precisely the details and durations of all the activities.

Estimating Our WorkUsing PERT

Role of Estimating in Planning• Planning is looking into the future

• The future is uncertain

• Thus, we cannot know (for sure) how much, how long, or how many

• Sizing and Estimates allow us to plan despite this lack of knowledge

– Sizing is about getting into the right ballpark

– Early estimates are about getting into the right section

– Later estimates are about getting into the right seat

• See “Cone of Uncertainty”

This isn’t estimating

• “Don’t worry, we will just wing it”

• “I remember last time -- it will be the same”

• Just ask someone who has done it

More Empirical

• Historical data

• Industry or company standards

• Use of real experts with actual knowledge

Problem surrounding estimating• No perfect foresight

• History is never really repeated

• The unforeseen usually does happen

• “Experts” do not agree

• Poor memory

• Projects without a history to rely upon

• People are different

An Example to Study

It is to be a wonderful warm spring Saturday, the first wonderful spring weekend of the year.

Tomorrow will be a perfect

day to get the yard mowed

Let’s see, what do we know

• ½ acre of lawn

• Self-propelled walking mower

• Weather is great

• Natasha wants us to take Felix to the lake for an afternoon family picnic

As you return from walking Fido Natasha asks a simple question

9 o’clockHow long until you are available

to drive to the lake?

Oh, uh, . . . . 2 hours

The trap has been set – you are already in trouble, Boris!!

What Should Go into a Good Estimate?

• An understanding of the work to be done

• Problem decomposition

• Careful thought surrounding what you do and do not know about the work pieces

• Smart communication of the estimate

Boris’ Problem:He did not think about

• First mowing of the year

• Mower is in the back of the ill-kept shed !

• Does he have gas; and oil ?

• Mower was not serviced in the fall !!!

• How long will the edging take ?

• What about the “weed-whacking” ?

Still think 2 hours ????Still think 2 hours ????

The other part of Boris’ problem

9 o’clockHow long until you are available

to drive to the lake?

Oh, uh, 2 hours

Good, I’ll have the kids ready to leaveat 11 o’clock

Let’s look at a technique to keep Boris out of trouble

and us !

The Development of PERT

• Program Evaluation and Review Technique

• Major US Navy project of 1950s -- Polaris

• Revolutionary advances in submarines, missiles and guidance systems

• Historical information will be of little value

• New estimating tool developed along with new PM methodology

Fundamental PERT Estimating Dilemma

How to develop reasonable estimates so we can

plan smartly

when we are short on information about the problem to be

solved?

The PERT Solution

• Take advantage of what you do have

• Smartly hedge your response

• Prepare to sense variations quickly

• Be ready to respond when new information becomes available

PERT estimating formula

Optimistic + 4 (Most Likely) + Pessimistic

Estimate =

6

• Pessimistic prediction

PERT is a 5-Input Model

• Most likely prediction

• Reasons to anticipate better performance

• Optimistic prediction

• Reasons to anticipate poorer performance

What is needed when preparing an estimate?

• Clear description of the work

• Understanding of the environment and tools you are going to use to solve the problem

• A desire for self-preservation

– Willingness to think about the problem before attempting to solve the problem

– Generally a poor estimate leads to underestimated the effort / time to complete the work

– This leads to long hours to meet these estimates

– At least this is what it means in IT

NJM WorksheetProject Work Estimating Sheet (PERT Methodology)

Project: Individual: Role:

Work to be Accomplished Logic and Adjustments

Phase   Activity/Task Reasons for a quicker time:

Assumptions

 Optimistic time: hours

Reasons for a slower time:

 Pessimistic time: hours

 Most likely time: hours

PERT calculated time:

TBD

hours 

Adjustment Logic: Final Estimate

What is Boris’ Real Work

• Get the tools (mower, edger, whacker) out of the shed

• Get the mower running

• Actually cut the lawn

• Edge the sidewalk and driveway

• Weed-whack around the shrubs, mailbox and light pole

• Put tools away

Discussionof the

Groups’ Work

Make Your Future Easier

• The best estimates start with documented experience on similar tasks

• This means we must do a good job of capturing actual time spent on current work

• Diligence in using the time reporting function of PlanView will make our future estimating life easier

Questions