Pair Programming: Why Have Two Do the Work of One

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Pair Programming Why Have Two Do the Work of One

• from
• Laurie Williams
• North Carolina State University

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Pair Programming
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Agenda

• Research/Findings
• Colocated Pairs
• Distributed Pairs
• Pair Interactions
• Sample Pairings
• Pair Rotation
• Summary

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Empirical Study for Validation

• Practice Summer 1999
• 20 Students (Sophomore/Junior)
• All worked collaboratively
• Generated more anecdotal/qualitative evidence
• Solo vs Pair Fall 1999
• 41 Students (Junior/Senior)
• 28 Worked Collaboratively
• 13 Worked Individually
• Software development process was controlled
• The only experimental variable pair-programming
• Quantitative Time, Quality, Enjoyment,
  Confidence

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Boxplot of Program Quality
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Boxplot of Student Time
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Collaboration by Phase
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Distributed Pair Programming

• Net Meeting
• Yahoo Messenger
• Graduate Object-Oriented class at NCSU
• 5-week project
• 132 students
• 34 distance students
• Teams of 2-4 students
• Colocated non-pairs (9 groups)
• Colocated pairs (16 groups)
• Distance non-pairs (8 groups)
• Distance pairs (5 groups)

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Productivity
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Quality
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Satisfaction with Working Arrangement
Very good Good Fair Poor
Non-pair colocated 46 40 11 3
Pair colocated 62 28 10 0
Non-pair distributed 45 37 18 0
Pair distributed 83 17 0 0
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Satisfaction with Communication
Very good Good Fair Poor
Non-pair colocated 57 26 11 6
Pair colocated 58 28 12 2
Non-pair distributed 41 41 14 4
Pair distributed 67 33 0 0
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Research Findings to Date

• Strong anecdotal evidence from industry
• We can produce near defect-free code in less
  than half the time.
• Empirical Study
• Pairs produced higher quality code
• 15 less defects (difference statistically
  significant)
• Pairs completed their tasks in about half the
  time
• 58 of elapsed time (difference not statistically
  significant)
• Most programmers reluctantly embark on pair
  programming
• Pairs enjoy their work more (92)
• Pairs feel more confident in their work products
  (96)
• Distributed pair programming is a viable
  alternative (worthy of much more research)

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How does this work?

• Pair-Pressure
• Keep each other on task and focused
• Dont want to let partner down
• Embarrassed to not follow the prescribed
  process
• Parkinsons Law Work expands to fill all
  available time.
• Pair-Negotiation
• Distributed Cognition Searching Through Larger
  Spaces of Alternatives
• Have shared goals and plans
• Bring different prior experiences to the task
• Different access to task relevant information
• Must negotiate a common shared of action
• Pair-Relaying
• Each, in turn, contributes to the best of their
  knowledge and ability
• Then, sit back and think while their partner
  fights on

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How does this work (part two)?

• Pair-Reviews
• Continuous design and code reviews
• Ultimate in defect removal efficiency
• Removes programmers distaste for reviews
• 80 of all (solo) programmers dont do them
  regularly or at all
• Debug by Describing
• Tell it to the Furby
• Pair-Learning
• Continuous reviews ? learn from partners
  techniques, knowledge of language, domain, etc.
• Between the two of us, we knew it or could
  figure it out
• Apprenticeship
• Defect prevention always more efficient than
  defect removal

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Vending Machine Program Responsibility
Assignment
UIMary
Buy Drink Joe
Data Structures Charlie
Machine Maintenance Sue
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Pair Rotation
UI Mary
Buy Drink Joe
Data Struct. Charlie
Mach Maint. Sue
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Expected Benefits of Pair-Programming

• Higher product quality
• Improved cycle time
• Increased programmer satisfaction
• Enhanced learning
• Pair rotation
• Ease staff training and transition
• Knowledge management/Reduced product risk
• Enhanced team building

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The Benefitsof Pair Programming

• Robert Kessler
• School of Computing
• University of Utah
• Special thanks to
• Laurie Williams
• North Carolina State University

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What Is Pair Programming?

• "Pair programming is a simple, straightforward
  concept. Two programmers work side-by-side at
  one computer, continuously collaborating on the
  same design, algorithm, code, and test. It
  allows two people to produce a higher quality of
  code than that produced by the summation of their
  solitary efforts."

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This Is Pair Programming
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This is NOT Pair Programming
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Pair Programming Has Been Around For a LONG TIME!
. . .
1945
1953
1997
1998
1999
2000
2001
2002

John von Neumann, recognized his own inadequacies
and continuously asked others to review his work.
Fred Brooks and many others are pair
programming, though they dont know there is a
name for it.
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Does Pair Programming Really Work?

• Empirical study by Laurie Williams at the
  university of Utah
• Practice Summer 1999
• 20 students (sophomore/junior)
• All worked collaboratively
• Generated more anecdotal/qualitative evidence
• Solo vs. pair Fall 1999
• 41 students (junior/senior)
• 28 worked collaboratively
• 13 worked individually
• Software development process was controlled
• The only experimental variable pair-programming
• Quantitative time, quality, enjoyment,
  confidence

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Findings 1 - Quality
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Findings 2 - Time
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Findings 3 and 4 Enjoyment and Confidence
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How Does This Work?

• Pair-Pressure
• Keep each other on task and focused
• Dont want to let partner down
• Embarrassed to not follow the prescribed
  process
• Parkinsons law work expands to fill all
  available time.
• Pair-Think
• Distributed cognition searching through larger
  spaces of alternatives
• Have shared goals and plans
• Bring different prior experiences to the task
• Different access to task relevant information
• Must negotiate a common shared of action
• Pair-Relaying
• Each, in turn, contributes to the best of their
  knowledge and ability
• Then, sit back and think while their partner
  fights on

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How Does This Work (Part Two)?

• Pair-Reviews
• Continuous design and code reviews
• Ultimate in defect removal efficiency
• Removes programmers distaste for reviews
• 80 of all (solo) programmers dont do them
  regularly or at all
• Debug by describing
• Tell it to the Furby
• Pair-Learning
• Continuous reviews ? learn from partners
  techniques, knowledge of language, domain, etc.
• Between the two of us, we knew it or could
  figure it out
• Apprenticeship
• Defect prevention always more efficient than
  defect removal

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Research Findings to Date - 1

• Strong anecdotal evidence from industry
• We can produce near defect-free code in less
  than half the time.
• Empirical study
• Pairs produced higher quality code
• 15 less defects (difference statistically
  significant)
• Observed pairs produced smaller (LOC) programs
• Pairs completed their tasks in about half the
  time
• 58 of elapsed time (difference NOT statistically
  significant)
• Most programmers reluctantly embark on pair
  programming
• Pairs enjoy their work more (92)
• Pairs feel more confident in their work products
  (96)

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Research Findings - 2

• Several educational studies underway
• University of California, Santa Cruz North
  Carolina State University
• What about pair learning?
• Anecdotal says that it works well
• What are the long-term issues?
• If you learn as a pair, can you work as a solo?
• Distributed pair programming studies underway
• North Carolina State University University of
  North Carolina-Chapel Hill
• Early results distributed pair programming is
  viable
• My experience
• Need to meet and know your pair
• Need a good tool like VNC and telephone
• Video not important

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Issues Workplace Layout
Bad
Better
Best
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Issues Partner Picking Principles
Expert paired with an Expert
Expert paired with a Novice
Novices paired together
Professional Driver Problem
Culture
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Issues Pair Rotation

• Ease staff training and transition
• Knowledge management/Reduced product risk
• Enhanced team building

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Issues Process

• Used in eXtreme Programming
• Used in the Collaborative Software Process
• Pair programming can be added to any process

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Expected Benefits of Pair Programming

• Higher product quality
• Improved cycle time
• Enhanced learning
• Pair rotation
• Ease staff training and transition
• Knowledge management/reduced product risk
• Enhanced team building
• Increased programmer satisfaction

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More Information

• Bob Kessler801-581-4653kessler_at_cs.utah.edu
• Laurie Williams919-513-4151williams_at_csc.ncsu.edu
  
• http//pairprogramming.com
• http//collaboration.csc.ncsu.edu/laurie