Agile Software Estimation

Agile Software Estimation
- Sunil Kumar

Agenda
What is an estimate?
Scenario
What are the factors influencing estimating?
How are agile projects estimated?
How Agile estimation solves common estimation problems?

How to estimate this task ?

What is an estimate?
Unbiased, analytical process to predict the duration or cost of a project

Estimation is the calculated approximation of a result which is usable even if input data may be incomplete or uncertain.

What does the definition mean?

By definition estimate is not accurate

Estimation is prediction not PLAN

Typical first estimate is off by factor of 4

We are not good in absolute measurement

We are good in comparing things

Estimates are not commitments

Time is not persistent

Scenario
You are told to estimate a project to “build a space shuttle that will land on moon”
You say “It will take 6 months to 2 years”
Your superior hears “It will take 6 months”. why? – optimism bias, organization, political and competitive pressures.

Scenario contd..
6 month estimate breakup
1 month design
4 months implementation
1 month testing

Scenario 1 contd..
Design takes 5 weeks, late by 1 week
How much did the project slip?
1 week?
25% ?

Answer
25% slip in project
25% of design = 1 week
25% of implementation = 1 month (approx 4 weeks)
25% of testing = 1 week
Total slip in project = 6 weeks

Factors influencing estimating

Assumptions (domain jargon)

Anchoring (by customers)

Same specification
One page spec
Group A
117 hours
7 Pages spec
Group B
173 hours

Irrelevant information for same spec
Group A
20 hours
added irrelevant details:
End user desktop apps
Usernames & passwords
Etc.
Group B
39 hours

Extra requirements
Requirements 1-4
Group A
4 hours
Requirements 1-5
Group B
4 hours
Requirements 1-5 but told to estimate 1-4only
Group C
8 hours

Given anchor
Group A
456 hours
Customer thinks 500
customer has no technical knowledge
Don’t let the customer influence you
Group B
555 hours
Same as B customer thinks 50
Group C
99 hours

Biased opinion

Dominating opinion

Re estimation is considered heretic by most organizations so we overestimate by buffering

Overestimation downside: Goldratt’s student syndrome
Eliyahu M. Goldratt

Competition, pressure from boss, peer-pressure, optimism bias, etc leads us to underestimate

Underestimating leads to project plan destruction

More bugs

Bad team health

More time in “status” meetings to discuss slippage

Time-based estimates are not additive for a team of varied skill set

What is the source of uncertainty in our projects?

Cloud of uncertainity (if the project is not well controlled)

Control the effects of overestimation and cloud of uncertainty using project planning and status visibility

Other factors influencing estimates
Unstable requirements
Forgetting to include the following while estimating
Version control overhead
Code review
Build, installing
More meetings
Sick leaves
etc

Always compare your estimates to your actuals or you’ll never be a better estimator
Wisdom = Experience + reflection
- Aristotle

Points to remember from Steve McConnell
Narrow ranges != greater accuracy
Don’t give off the cuff estimates
Precision is not accuracy. The project will not take 233.725 hours
Find something meaningful to count and keep a record of it.
Use expert judgement only as a last resort

Estimation techniques
Expert opinion
Analogy
Educated guess
Disaggregating
Planning poker – Agile estimation

Planning poker
http://www.planningpoker.com/
Consensus-based estimation technique for estimating
First described by James Grenningand later popularized by Mike Cohn in the book Agile Estimating and Planning

Planning Poker
Estimated in story points for user stories*
It is most commonly used in agile software development
First described by James Grenning in 2002 and later popularized by Mike Cohn in the book “Agile Estimating and Planning”
For Eg: the deck contains the following cards: 0, ½, 1, 2, 3, 5, 8, 13, 20, 40, 100.
User stories are user requirements of form "As a <Some Role> I want <Some Need> so that <Some Benefit>”

Planning Poker
Each person gets a deck of cards.
The story to be estimated is read to all.
Attendants ask clarifications for the item.
Each person selects a card and puts it on the table facing down.
When everyone is done, cards are exposed.
If the estimations do not match a short discussion is done.
Timer is started for discussion and discussion must cease when it runs out -> Goto 4.
Handle next item.

Why planning poker works ?
Those who do the work estimate it.
Emphasizes relative estimation
Estimates are within one order of magnitude.
Reduces anchoring - Everyone's opinion is heard.
Modeled for open discussion – forces thinking.
It’s quick & fun !

At the beginning of the project
Use story trawling to prioritize tasks.

How to calculate time?
Time (in no of iterations) =
( No of Story points / Velocity of each sprint/iteration)

Velocity
How many points can the team complete in one iteration.
Easy to measure.
Fixes estimation errors.
Easily reflects the project status.
Primary parameter in planning.

How Agile estimation solves common estimation problems?

Assumptions reduced by constant communication

Anchoring is eliminated by not estimating in time but relatively

Cross-functional team while estimating shield from biased opinion

Blind vote and consensus rules out dominating opinion

Daily standup, self-organization and burndown charts reduce affect of overestimation

Estimation is based on team velocity for a sprint, this reduces underestimation

References
Agile estimation and planning – Mike cohn (http://www.mountaingoatsoftware.com/books/1-agile-estimating-and-planning)
http://www.slideshare.net/codeburns/the-art-of-estimation-presentation
http://www.slideshare.net/aviram37/agile-estimation-sd-forum
Software Estimation: Demystifying the black art – Steve McConnell (http://www.stevemcconnell.com/est.htm)

Questions?

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Agile Software Estimation

by Sunil Jakkaraju on Aug 17, 2009

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Agile Software Estimation — Presentation Transcript