guesstimate - some thoughts on estimation in software development

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GuesstimatePeter Rubarth, 2014

Prediction is very hard, especially if it‘s

about the futureNils Bohr

Exercise 1 – Expert estimation

Write down your estimates for the following facts:

1. Length of German border (in km)2. Amount of water in Bodensee lake (in l)3. Dollars (as notes) in circulations within the USA in 2004 (in

$) 4. Birth year of Alexander the Great (year)5. World wide revenue with movie “Titanic” (in $)6. Latitude of Shanghai (in degrees)7. Temperature on the surface of the sun (in °C)8. Number of bacteria in human intestines9. Number of works of Ludwig van Beethoven10. Expanse of Asia (in km^2)11. Number of stars in Milky Way12. Number newly published books in Germany 2004-200713. Area covered by Hamburger Hafencity including water area

(in ha)

Thank you @projectzone - http://yourprojectzone.com/2014/03/30/uebung-team-estimation-game

Why do we estimate?

●Prepare project bid●Plan time, resources, …●Foster discussion●Determine economic

feasability●Someone told us so●…

What do we estimate?

●Time

●Effort

●Complexity

How do we estimate?

Expert estimation

●Ask someone who should know

Formal model

• COCOMO 2, Function Points, IFPUG FPA, LOC, COSMIC Full Function Point (FFP) …

What could go wrong?

Insufficient data

Negotiation● Now cut that in half and we have a deal

Estimates become targets

● But you’ve said it will take only so long!

Work expands so as to fill the time

available for its completion.

● Parkinson‘s Law

This is why buffers (or the Project Managers‘ multiplier) don‘t work.

Cycle of Mistrust

Deliver the wrong thing, or late

Trust breaks down

Commitments of

scope and time

Focus on schedule

© Copyright Neil Killick, Iterative, 2013

Good Practise

Clarify objectives

• For which purpose?

• What are the risks and mitigation strategies?

• Awareness of the nature of estimations?

Provide ranges not a single value

Likely effort from … to ….

Helps to communicate that an estimate is not a guarantee

Use indirection, avoid direct time estimates

• Abstract units such as Story Points, Ideal Days or T-Shirt sizes help to communicate uncertainty

• Support empiric forecasting

Explicitly state assumptions

Provide a disclaimer:• Which assumptions • Use approach and data• Risks and possible impact

At least you have told `em

Review and update your estimates

• Use what you have learned• Do not hide unwelcome

news• Burnt hours are a bad

progress indicator

The evil of Fixed Price Contracts

Knowing it will take longer does not help, because everything is fixed (unless people really idled before)

Strong incentive to cut corners and damage quality

Even better practise

• FOCUS ON VALUE• DELIVER SMALL SLICES• DELIVER EARLY &

FREQUENTLY• CUSTOMER

COLLABORATION© Copyright Neil Killick, Iterative, 2013

EMPIRICISM

• Use actual results to predict progress

Useful Methods

Group Estimation

Don‘t rely on a single opinion

Methods:• Wideband Delphi• Planning Poker• Affinity Mapping

Analogy Method

• Compare project to previous experience

• Use checklist to compare and classify on different dimensions

• Only useful if sufficient similarity

Affinity Estimation

• Silently order items relative to each other

• Build clusters

• Apply appropriate scale

Now it‘s your turn!

Exercise 2 –Affinity Estimation

1. Take first item and place it in the

center

2. Take turns and position subsequent

item relative to existing items

3. Reorder if you disagree

4. Do not discuss!

Exercise 2 – Affinity estimation

Write down your estimates for the following facts:

1. Length of German border (in km)2. Amount of water in Bodensee lake (in l)3. Dollars (as notes) in circulations within the USA in 2004 (in

$) 4. Birth year of Alexander the Great (year)5. World wide revenue with movie “Titanic” (in $)6. Latitude of Shanghai (in degrees)7. Temperature on the surface of the sun (in °C)8. Number of bacteria in human intestines9. Number of works of Ludwig van Beethoven10. Expanse of Asia (in km^2)11. Number of stars in Milky Way12. Number newly published books in Germany 2004-200713. Area covered by Hamburger Hafencity including water area

(in ha)

Thank you @projectzone - http://yourprojectzone.com/2014/03/30/uebung-team-estimation-game

Exercise 2 –Solution

Find the solution at

http://yourprojectzone.com/2014/03/30/

uebung-team-estimation-game/

Thank you!Twitter: #PRubarth