Range estimation in Scrum

Building a more accurate burndown

Using Range Estimation in Scrum

Agile 2010 ConferenceAugust 2010

Arin Sime

434 996 [email protected]

Pitfalls of traditional estimation

techniques

How long does it take you to get to work?

traffic

optimisticmethod of travel

every day?

68%http://www1.standishgroup.com/newsroom/chaos_2009.php

A little about me…Senior Consultant, OpenSource Connections

in Charlottesville, Virginia

Masters in Management of I.T., University of Virginia, McIntire School of Commerce

We tweaked our Scrum process to incorporate Range Estimation based on my studies at Uva

Please take the Estimation Survey: http://www.surveymonkey.com/s/SWNNYQJ

http://www.surveymonkey.com/s/SWNNYQJ

The root of all estimation evil: Single point estimates

Chart taken from: Software Estimation, Steve McConnell, Figure 1-1, p6

“A single-point estimate is usually a target masquerading as an estimate.”-Steve McConnell

A realistic estimate distribution

Chart taken from: Software Estimation, Steve McConnell, Figure 1-3, p8

“There is a limit to how well a project can go but no limit to how many problems can occur.”-Steve McConnell

Nominal Outcome(50/50 estimate)

Reasons we are wrong so often

Different information

Different methods

Psychological Biases

The Expert Problem

Bias in Estimation

Imagine this scenario:

“Can you build me that CMS website in 2 weeks?”

How would you respond?

What estimate would you give?

Bias in Estimation

By supplying my own estimate (or desire) in my question, I have anchored your response.

This is called “The anchoring or framing trap”

“Because anchors can establish the terms on which a decision will be made, they are often used as a bargaining tactic by savvy negotiators.”

From “The Hidden Traps in Decision Making” from Harvard Business Review, 1998, John Hammond, Ralph L. Keeney, and Howard Raiffa

You’re not as good as you think

“The Expert Problem”

Experts consistently underestimate their margins of error, and discount the reasons they were wrong in the past.

Excuses for past mistakes:• You were playing a different game • Invoke the outlier• “Almost right” defense

The Black Swan: The impact of the Highly Improbable,

by Nassim Nicholas Taleb, 2007, Chapter 10: The Scandal of Prediction

The best protection

“The best protection against all psychological traps – in isolation or in combination – is awareness.”

From “The Hidden Traps in Decision Making” from Harvard Business Review, 1998, John Hammond, Ralph L. Keeney, and Howard Raiffa

Agile estimation techniques

How agile already avoids pitfalls

Encourages team airing of estimates

Done before assignment of tasks

Scrum poker

How agile already avoids pitfalls

Separates story from time units, more relative

Story Points& Velocity

Image from: http://leadinganswers.typepad.com/leading_answers/2007/09/agile-exception.html

Agile and Scrum can run into other

pitfalls though…

Potential pitfalls:

Single-point estimates

What about Risk?

Implies a set delivery of features

Story points are hard to explain

Better accuracy using range estimation

The Cone of Uncertainty

http://www.construx.com/Page.aspx?hid=1648

Range estimation …

• Recognizes uncertainty• Alleviates our tendency towards optimism• Incorporates risk• Allows for better financial projections• Better informs our bosses and clients

Incorporating range estimation

into Scrum

Incorporating range estimation into Scrum

Team originally estimated 108 hours

• Range estimate went from 114-245 hours.

• Note the single point was a low estimate!

• They were able to finish original tasks a little early

Range estimation in Scrum Poker

It’s very simple – just hold two cards instead of one!

The same rules apply about creating discussion between low and high estimators, but you might resolve them differently...

On the high end

On the low end

On the high end

The likely discussion:Hey Orange, why do you say

“2”? Yellow and Blue both say “5”.

Likely Outcome: 3 or 5

Middle of the road



Still middle of the road, but Green recognizes some risk

Orange sees this as really easy

Blue sees this as more complicated

The likely discussion:Orange and Blue need to

compare their visions for this task.

Likely Outcome: 8-13?

Red and Blue no longer agree: Red is confused or sees big risks

Using ranges in your task list

Using ranges in your task list

Enter Low/High

=(Lo*0.33)+(Hi*0.67)

Sums of Lo, Hi, 2/3; then trend them to zero

update daily

Using ranges in your burndown

Ranges help to highlight obstacles and know when to cancel an iteration

We were able to improve on the next iteration, but it was still hard

Ranges help reinforce obstacles

Obstacle removedObstacle removed

Why 2/3?

Source on PERT: Software Estimation, Steve McConnell, p109

Because it is both simple and pessimistic

PERT does a similar thing:Expected = [BestCase + (4*MostLikely) + WorstCase] / 6

Using ranges to better

communicate

Using range estimation to communicate risk

• Size of your range communicates the risk of your task

• May encourage you to break up tasks, or better define them.

• Scrum is all about better communication with the customer – so are ranges

YouYour BossBig Boss

How long?How long?

Um… 2 daysUm… 2 days

4 days4 days

Do you know your fudge factor?


How long?How long?

2-4 days2-4 days2-4 days2-4 days

Ranges help you control your fudge factor


Another example: Use ranges to better empower

your boss or client


Perfect – Do it!Perfect – Do it!

2 days2 days

How long?How long?How much for X?How much for X?

Actually … 4 daysActually … 4 days

4 days later…

GRRRGRRR

2 days * rate2 days * rateBudget Left: 2

days

Budget Left: 2

days

Umm…..Umm…..


Instead….


No thx, do something easier

No thx, do something easier

2-4 days2-4 days

How long?How long?How much for X?How much for X?

Done!Done!

2 days later…

YES!YES!

2-4 days * rate2-4 days * rateBudget Left: 2

days

Budget Left: 2

days

Potential pitfalls of range estimation


Really Wide Ranges

Not everything can take 2 – 200 hours or you lose

all credibility

Really Wide Ranges

Not everything can take 2 – 200 hours or you lose

all credibility


Bosses who don’t get it

You’re going to have to sell them on how your estimates will improve

their decision making ability.

Bosses who don’t get it

You’re going to have to sell them on how your estimates will improve

their decision making ability.


Pushed back deadlines

Ranges are not an excuse to always miss deadlines. But they do make it less of a surprise, and encourage you to be more cautious.

Pushed back deadlines

Ranges are not an excuse to always miss deadlines. But they do make it less of a surprise, and encourage you to be more cautious.


Is 2/3 the new single-point?

Be careful not to just start treating the 2/3 calculated estimate, use the ranges.

Is 2/3 the new single-point?

Be careful not to just start treating the 2/3 calculated estimate, use the ranges.

Range estimation in Scrum

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