Range estimation in Scrum

Building a more accurate burndown Using Range Estimation in Scrum Agile 2010 Conference August 2010 Arin Sime 434 996 5226 [email_address]

Pitfalls of traditional estimation techniques

How long does it take you to get to work? traffic optimistic every day? method of travel

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

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
Range estimation in Scrum Poker 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

Range estimation in Scrum Poker 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 removed

Why 2/3?
Because it is both simple and pessimistic
PERT does a similar thing:
Expected = [BestCase + (4*MostLikely) + WorstCase] / 6
Source on PERT: Software Estimation , Steve McConnell, p109

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

How long? Um… 2 days 4 days Do you know your fudge factor? You Your Boss Big Boss

How long? 2-4 days 2-4 days Ranges help you control your fudge factor You Your Boss Big Boss

Another example: Use ranges to better empower your boss or client You Your Boss Big Boss

Perfect – Do it! How long? How much for X? GRRR Umm….. You Your Boss Big Boss 2 days Actually … 4 days 4 days later… 2 days * rate Budget Left: 2 days

Instead…. You Your Boss Big Boss

No thx, do something easier How long? How much for X? YES! You Your Boss Big Boss 2-4 days Done! 2 days later… 2-4 days * rate Budget Left: 2 days

Potential pitfalls of range estimation

Potential pitfalls of range estimation Really Wide Ranges Not everything can take 2 – 200 hours or you lose all credibility

Potential pitfalls of range estimation Bosses who don’t get it You’re going to have to sell them on how your estimates will improve their decision making ability.

Potential pitfalls of range estimation 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.

Potential pitfalls of range estimation 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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