Attack Sources of Variability to Improve Predictability
Kanban Recipe for Success: Step Six
Jason [email protected]
[email protected]@jchyip
http://jchyip.blogspot.com
HOMEWORK CHECK
What step(s) did you take to start prioritising?
The Recipe for Success
1. Focus on Quality2. Reduce WIP3. Deliver Often4. Balance Demand Against Throughput5. Prioritise6. Attack Variability to Improve
Predictability
WHAT IS VARIABILITY?
WHY VARIABILITY?
“We cannot add value without adding variability, but we can add variability without adding value.”
Don Reinertsen, The Principles of Product Development Flow
“Variability results in more work-in-progress and longer lead times.”
David Anderson, Kanban
Variability leads to buffers and bottlenecks
http://flic.kr/p/4QofnD
“Consistency leads to better programs. If formatting varies unpredictably, or a loop over an array runs uphill this time and downhill the next, or strings are copied with strcpy here and a for loop there, the variations make it harder to see what’s really going on. But if the same computation is done the same way every time it appears, any variation suggests a genuine difference, one worth noting.”
Brian Kernighan and Rob Pike, The Practice of Programming
Paying attention to variability helps you to see problems
SOURCES OF VARIABILITY
Types of variation• Internal
– Due to the design of the system– Variation is random with no clear assignable cause– Address this by changing the policies and process (aka
“rules of the game”)
• External– Variation caused by events or aspects that are outside your
control– It is possible to assign a cause (aka the external event)– Address this by having systems and structures to “roll with
it” (aka risk management)
Various ways to talk about variation
• Shewart– Chance-cause (random and inherent to system design) vs assignable-
cause (cause-and-effect with external event)
• Alpert / Deming– Common-cause (common to all similarly designed systems) vs
special-cause (new knowledge or event that is different to how the system normally works)
• Feigenbaum– Usual (the variation you’ve learned to expect) vs unusual (any
variation that is not expected) (Also normal vs abnormal)
• Wheeler– Routine (predictable variation characteristic of common causes) vs
exceptional (unpredictable variation as the result of an assignable cause)
http://jchyip.blogspot.com.au/2010/05/different-ways-to-describe-causes-of.html
Internal sources of variability in software development
• Software development process• Project management process• Organisational systems and
structures• Capability of team members• Technology choice
“Simply changing an existing process policy can dramatically reduce sources of variability that affect predictability.”
David Anderson, Kanban
ASIDE: VARIATION IS NOT INHERENTLY EVIL
“We cannot add value without adding variability, but we can add variability without adding value.”
Don Reinertsen, The Principles of Product Development Flow
Which choice has the least variability?
Choice Stakes Payoff Probability
A $15 000 $100 000 50%
B $15 000 $20 000 90%
C $15 000 $16 000 100%
Derived from The Principles of Product Development Flow by Don Reinertsen
Which is the best economic choice?
Choice Stakes Payoff Probability Expected Value
A $15 000 $100 000 50% $35 000
B $15 000 $20 000 90% $3 000
C $15 000 $16 000 100% $1 000
Derived from The Principles of Product Development Flow by Don Reinertsen
Higher variability raises pay-off
From The Principles of Product Development Flow by Don Reinertsen
Don’t “minimise variability” nor “maximise variability”
but rather optimise variability based on context
Don Reinertsen’s two main approaches for dealing with variability
1. Change the amount of variability2. Change the economic consequences
of the variability
TACTICS FOR REDUCING VARIABILITY
Standardise work item size
• Standardise the format (e.g., As a…I want…in order to…)
• Limit the number of types (e.g., S, M, L vs 0 – 100)
Which betting approach has less variation?
1. Flip a coin. Heads, you win $100; tails, you lose $100.
2. Flip a coin 4 times. Each time you flip, heads, you win $25; tails, you lose $25.
Option 1: Chance of losing $100 is 50% (1 in 2)Option 2: Chance of losing $100 is 6.25% (1 in 16)
Derived from The Principles of Product Development Flow by Don Reinertsen
Many small experiments produce less variation than one big one
If it varies too much, do it more often
http://martinfowler.com/bliki/FrequencyReducesDifficulty.html
Automate
Practice
Reuse
… but decide based on economics, not “maximising reuse”
http://en.wikipedia.org/wiki/Vacuum_tube
Pursue high quality
• Peer reviews• Pair programming• Unit tests• Continuous integration• Small batch sizes• Highly cohesive, loosely coupled
architectures
Remove unnecessary ambiguity
Put limits on expedite requests
Process behaviour (aka control) charts
TACTICS FOR IMPROVING THE CONSEQUENCES OF VARIABILITY
“A [schedule] buffer converts uncertain earliness to certain lateness. Thus, it is generally a bad idea to trade cycle time for reduced variability in cycle time.”
Don Reinertsen, The Principles of Product Development Flow
Rapid feedback
• Think Mean Time to Recover vs Mean Time to Failure
Substitute cheap variability for expensive variability
From The Principles of Product Development Flow by Don Reinertsen
HOMEWORK
What is the smallest step you could take to move 1
level up (or more)?
What is your plan to start that step tomorrow?