Software Development Estimation

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• Software Development Estimation

Dark Art or Science?
Stefan Kiryazov (Vereo, Wizefish)
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Introduction

• Target audience
• Senior software developers
• Technical leaders
• Project managers
• High level managers
• Customers
• Required background skills
• Familiarity with the software development process

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Contents

• Causes for Uncertainty
• Presenting Estimates
• Estimation Process

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Background

• Why is estimating important?
• A foundation for efficient development
• Estimate too high Parkinsons law
• Estimate too low inefficient planning
• Is perfect estimating possible?
• The software estimating story

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Cost Budgeting
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Causes for Uncertainty

• Will the customer want Feature X?
• Will the customer want the cheap or expensive
  version of Feature X?
• If we go for the cheap, will he/she want the
  expensive one later after all?
• How will Feature X be designed?
• How long will it take to fix the bugs in Feature
  X?
• How long will it take to integrate Feature X?

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Causes for Uncertainty

• Software development a process of gradual
  refinement
• The perfect estimate is doing the project work
  itself
• The earlier, the less precise

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Estimate Convergence Graph
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• It is the mark of an instructed mind to rest
  satisfied with the degree of precision which the
  nature of the subject admits and not to seek
  exactness when only an approximation of the truth
  is possible
• Nichomachean Ethics, Aristotle

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The Schedule Graph
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Optimistic Schedule Graph
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Presenting Estimates

• Presentation styles
• Plus/minus
• Conditions
• Cases
• Ranges
• Avoid overprecise estimates
• Accuracy vs precision
• Use coarse periods

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Estimation Process

• Size estimation
• Effort estimation
• Schedule estimation

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Size Estimation

• What is size?
• Function points
• Lines of code
• Custom measurement
• Compare with past projects
• Compare with documented data, not personal memory

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Effort Estimation

• Derived from size estimate
• No off-the-cuff estimates!
• Even with conditions!
• Estimate at high level of detail
• Law of large numbers

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Effort Estimation

• Dont omit common tasks
• Developer based estimates
• Sanity checking
• Commitment-based estimates
• Compare estimates

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The Cost Graph
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Schedule Estimation

• The nominal schedule
• Schedule 3 Effort1/3
• Schcedule months, Effort - manmonths
• Schedule compression
• Compression Factor (CF) Nominal / Compressed
• Compression increases cost!
• Compressed cost Initial cost / CF

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Questions

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