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Guesstimation

2008-09-24 08:43:54

At the initial planning stage the main objective is to get a realistic estimate

of the time involved in the project. You must establish this not only to assist

higher management with their planning, but also to protect your team from being

expected to do the impossible. The most important technique for achieving this

is known as: guesstimation.

Guesstimating schedules is notoriously difficult but it is helped by two

approaches:

make your guesstimates of the simple tasks at the bottom of the work break

down structure and look for the longest path through the sequence diagram

use the experience from previous projects to improve your guesstimating

skills

The corollary to this is that you should keep records in an easily accessible

form of all projects as you do them. Part of your final project review should

be to update your personal data base of how long various activities take.

Managing this planning phase is vital to your success as a manager.

Some people find guesstimating a difficult concept in that if you have no

experience of an activity, how can you make a worthwhile estimate? Let us

consider such a problem: how long would it take you to walk all the way to the

top of the Eiffel Tower or the Statue of Liberty? Presuming you have never

actually tried this (most people take the elevator part of the way), you really

have very little to go on. Indeed if you have actually seen one (and only one)

of these buildings, think about the other. Your job depends upon this, so think

carefully. One idea is to start with the number of steps - guess that if you

can. Notice, you do not have to be right, merely reasonable. Next, consider the

sort of pace you could maintain while climbing a flight of steps for a long

time. Now imagine yourself at the base of a flight of steps you do know, and

estimate a) how many steps there are, and b) how long it takes you to climb

them (at that steady pace). To complete, apply a little mathematics.

Now examine how confident you are with this estimate. If you won a free flight

to Paris or New York and tried it, you would probably (need your head examined)

be mildly surprised if you climbed to the top in less than half the estimated

time and if it took you more than double you would be mildly annoyed. If it

took you less than a tenth the time, or ten times as long, you would extremely

surprised/annoyed. In fact, you do not currently believe that that would happen

(no really, do you?). The point is that from very little experience of the

given problem, you can actually come up with a working estimate - and one which

is far better than no estimate at all when it comes to deriving a schedule.

Guesstimating does take a little practice, but it is a very useful skill to

develop.

There are two practical problems in guesstimation. First, you are simply too

optimistic. It is human nature at the beginning of a new project to ignore the

difficulties and assume best case scenarii - in producing your estimates (and

using those of others) you must inject a little realism. In practice, you

should also build-in a little slack to allow yourself some tolerance against

mistakes. This is known as defensive scheduling. Also, if you eventually

deliver ahead of the agreed schedule, you will be loved.

Second, you will be under pressure from senior management to deliver quickly,

especially if the project is being sold competitively. Resist the temptation to

rely upon speed as the only selling point. You might, for instance, suggest the

criteria of: fewer errors, history of adherence to initial schedules, previous

customer satisfaction, "this is how long it takes, so how can you trust the

other quotes".