Range estimation in Scrum
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Transcript of 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
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
Range estimation in Scrum Poker
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 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?
YouYour BossBig Boss
How long?How long?
2-4 days2-4 days2-4 days2-4 days
Ranges help you control your fudge factor
YouYour BossBig Boss
Another example: Use ranges to better empower
your boss or client
YouYour BossBig Boss
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…..
YouYour BossBig Boss
Instead….
YouYour BossBig Boss
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
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
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.
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.
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.
Is 2/3 the new single-point?
Be careful not to just start treating the 2/3 calculated estimate, use the ranges.
Further Reading