The Art of Software Estimation

What is estimation?

• Size and scope
• Effort
• Time
• Schedule
• Cost

Elements of an estimate

• Source Lines of Code and Function Points
• Effort and efficiency metrics

Establishing the estimation process

• Balancing exactness and predictions
• Iterating for greater precision

Defining the software environment

• Identifying the software project phases: define, design, code, test and implement
• Considering varying software development methodologies
• Factoring in the development environment: programming language, skill levels and resources

Delivering Expert Judgement Estimates

Analysing project documents

• Determining information gaps
• Identifying assumptions, constraints and risks

Acquiring expert perspectives

• Conducting an interview with an expert
• Asking clarifying questions
• Incorporating the information into estimates

Developing the estimate

• Synthesising the estimate from gathered input
• Evaluating your confidence in the estimate

Calibrating Estimates with Historical Data

Analysing historical data

• Evaluating similarities and differences between current and previous projects
• Extracting relevant metrics

Refining the initial estimate

• Calculating the estimate using appropriate measures
• Incorporating all software life cycle activities in the estimate
• Checking your estimate against historical data

Fine Tuning with Component Methods

Interpreting the work breakdown structure (WBS)

• Identifying the elemental components
• Recognising omissions in the WBS

Evaluating components and activities

• Choosing estimation metrics
• Applying metrics systematically
• Consulting with team members
• Eliciting single-point estimates
• Performing the PERT (three-point) methodology

Pulling it all together

• Adding up the component estimate
• Factoring in project complexities
• Comparing with the previous iterations

Improving the Estimate Using Software Metrics

Determining what to count

• Lines of code
• Function Points
• Use case points
• Story points
• Calculating simple probability statistics and standard deviation

Converting metrics into effort

• Deriving metrics from internal historical data
• Computing effort using industry standard formulas

Developing Effective Time, Schedule and Cost Estimates

Estimating productivity

• Deriving common conversion metrics
• Determining productivity metrics

Calculating time and cost

• Applying productivity metrics to the project
• Building a schedule
• Producing a time estimate
• Generating the project cost estimate

Communicating the estimate to management

• Documenting the estimate according to the size and complexity of the project
• Presenting and defending the estimate