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* This
porridge is just right!**.*

**Goldilocks**

**Fictitious Fairy Tale
Character**

*
The first bowl of chocolate pudding was too hot, but
Goldilocks ate it all anyway because, hey, it's
chocolate pudding, right?*

**Mo Willems****,
American Writer and Animator (1968 - ) **

**
Goldilocks and the Three Dinosaurs**

The Goldilocks estimate

Phillip G. Armour

Communications of the ACM, 2012

Communications of the ACM, 2012

**The Drive By Estimate
**

Ever had your boss say:

"...We don't have time to do all this estimation work, just give me a number..."?That's a

Destimate. No prep, no calculation, no data. Just a quick, inglorious, and unvarnished opinion.rive-By

**
The
Never-Ending Estimate
**

Ever had your boss say:

"...we've got to make sure this estimate is completely accurate. Let's work on it until it's perfect..."This is is the

estimate. To make an estimate truly "accurate" we have to remove all the uncertainty. The only way to do that is to go and actually run the project. But if you're waiting for the estimate to decideNever-Endingyou want to run the project,... then you're stuck.if

**
Not Too Little, Not Too Much
**

Clearly, "too little" is not enough, while "too much" is, well, too much. so the optimal amount of work to be done on an estimate is somewhere between these two values...

...but * where*
exactly?

This graph shows the components of net cost of an estimate. The declining exponential curve is the cost of a "bad" estimate--the longer time and more effort we spend producing an estimate, the 'better" it will be and the more likely that business decisions made based on the estimate will be sound and won't incur unexpected costs. The straight line is the cost of producing an estimate (assuming that a constant number of people are employed working on it.

The "Goldilocks" point is the green area in the middle. Here's how to calculate the cost of this point:

Cost_of_Estimate_ = Lifecycle_Phase *
Target_Cost_of_the_Project^{0.35}

Where

Lifecycle_Phaseis the phase in which the project is being estimated. It has typical values of:Early Lifecycle (feasibility or "what if?" estimates. . . . . . . . . . . . 24

Budgeting estimates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Definitive or Planning estimates. . . . . . . . . . . . . . . . . . . . . . . 115The

Target Cost of the Estimateis just what weto spend on the total projectwant

Example:A project with a target cost of $10m requiring a planning estimate should expect to spend around $32k to produce the estimate (try it!).

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