IKnowHow

Project Management Office

30 September 2013

Estimate Activity

Durations

Knowledge Area: Time Management

Who should do the estimation?

The estimators should be those who will be

doing the work, when possible.

The estimators are more often the members of

the project team who are most familiar with the

work to be done.

Padding

I have no idea how long it will take. I don’t even know what I am asked to do. So what do I say?

I will take my best guess and double it…

A pad is extra time or cost added to

an estimate because the estimator

does not have enough information

If your estimates are padded, you have

a schedule or budget that no one believes

The project manager’s role

Provide the team with information to properly

estimate each activity

Prevent padding

Complete a sanity check of the estimates

Make sure assumptions made during

estimating, are recorded for later review

The customer

If a customer want the shortest possible

schedule, they should not pressure you to

lower your estimates or to provide them with

misleadingly precise estimates.

Estimating activity techniques

I. One-Point Estimating

II. Expert judgment / Expert advice

III. Analogous Estimating (Top-down)

IV. Parametric Estimating

V. Three-Point Estimates

VI. Reserve Analysis

VII. Delphi & Wide-band Delphi Technique

One-point Estimating

The estimator submits one estimate per activity (…

that activity will take 5 days)

Maybe based on expert judgment, historical info or it

could be just a guess

Should only be used

for projects that do

not require a detailed

schedule

• Forces people to pad their estimates

• Hides important info about risks from the project

manager

• It can result in a schedule that no one believes

• Often results in the estimators working against the

project manager to protect themselves

• If an activity is estimated to 20d and is completed in

15d, it can make the estimator look untrustworthy.

Expert judgment

Expert judgment guided by historical information, can

provide estimates from prior similar projects and

experience

Vendors may be a good source

Analogous Estimating (Top-down)

Analogous estimating uses parameters such as

duration, budget, size, complexity from previous

similar projects, as the basis for estimating the same

parameters for a future project.

It is frequently used to estimate a project when there is

a limited information about the project (for example in

the early phases of a project).

It is generally less costly and time consuming than

other techniques, but is also less accurate.

Parametric Estimating

Uses statistical relationship between historical data

and other variables

For example, the estimator may use measures like time

per line of code

Three-point Estimates

The accuracy of activity duration estimates can be

improved by considering uncertainty and risk

This concept originated with the Program Evaluation

and Review Technique (PERT), which uses three

estimates to define an approximate range for an

activity’s duration.

PERT calculates a risk based Expected activity

duration using a weighted average of these three

estimates)

E = (o + 4m + p) / 6

where E is Estimate; o = optimistic estimate; p = pessimistic

estimate; m = most likely estimate

Reserve Analysis

Duration estimates may include contingency reserves

(time reserves or buffers) into the overall project

schedule to account for schedule uncertainty

May be a percentage of the estimated activity duration,

or a fixed number of work periods.

We should establish a reserve risk remaining after the

risk management process. THIS IS DIFFERENT THAN

PADDING

Delphi & Wide-band Delphi

Delphi is a group technique that extracts and

summarizes the knowledge of a group. The group are

experts who participate anonymously in order to

achieve consensus.

A request of information is sent to the experts, their

responses are compiled and the results are sent back

for further review until consensus is reached.

Usually uses three passes and the average of the third

guess is used as the groups estimate.

Wide-band Delphi combines Delphi and Three-

Point Estimating

Estimating Tips

Avoid off-the-cut estimates

Allow time for the estimate and plan it

Use data from previous projects

Use developer-based estimates

Estimate by walk-through

Estimate by categories

Estimate at a low level of detail

Don’t omit common tasks

Use several estimation techniques and compare

results

Rushedestimates are

inaccurate estimates

Sources:

A Guide to the Project management Body of Knowledge, 4th edition

(Project Management Institute)

Effective Software Project Management (2006, Robert Wysocki)

Rapid Development (1996, Steve McConnell)

PMP exam prep, 7th edition (Rita Mulcahy)

Senior Project Manager

Stavros Labrou