Estimation for Software project development is the process of predicting the most realistic amount of effort (expressed in terms of person-hours or money) required to develop or maintain software based on incomplete, uncertain and noisy input. Project managers, stakeholders, and staff members can use software metrics to more accurately estimate progress toward project milestones, especially when historical or trend data are available.
Attributes of a software project would be measured:
- Cost, in terms of staff effort, phase effort and total effort
- Defects found or corrected, and the effort associated with them
- Process characteristics such as development language, process model and technology
- Project dynamics including changes or growth in requirements or code and schedule
- Project progress (measuring performance against schedule, budget, etc.)
- Software structure in terms of size and complexity
Project Estimation Process
There are well know process for estimations but it will not suit for project, client or company. Each project will different level of attributes of a software project.
Project Estimation: A Four-Stage Process [1]
- Initiation: Analogous estimates are used at this phase. They are big picture estimates based on similar projects that have been documented in the corporation’s project archives. These estimates are stated as order of magnitude estimates.
- Early Planning: Project-level and major deliverable-level estimates are often analogous or 3-point estimates. During this phase, you may also use parametric estimating techniques.
- Final project plan: You use information from the team members and include them in bottom-up estimating of their deliverables.
- Weekly status: You use rolling estimates every week until the project is complete.
Project Estimation: A Basic Eight Stage Process [2]
- Understand your team’s expertise & job responsibilities
- Become the go-to expert of your company’s project process
- Broaden your PM skill set
- Study estimation history
- Ask more of the right questions
- Apply a work breakdown structure
- Estimating projects with Team-Gantt
- Get to planning and estimation
Ten Step Project Estimation Process [3]
- Establish estimate scope
- Establish technical baseline, ground rules & assumptions
- Collect data
- Size software
- Prepare baseline estimates
- Quantify risks & risk analysis
- Review, verify, validate estimate
- Generate a project plan
- Document estimate & lessons learned
- Track project throughout development
Estimation approaches
There are many ways of categorizing estimation approaches
- Expert opinion - This is an estimate based on recollection of prior systems and assumptions regarding what will happen with this system, and the experts’ past experience.
- Analogy - A method by which you compare a proposed component to a known component it is thought to resemble, at the most fundamental level of detail possible. Most matches will be approximate, so for each closest match, make additional size adjustments as necessary. A relative sizing approach such as SEER-AccuScope can provide viable size ranges based on comparisons to known projects.
- Formalized methodology - Use of automated tools and/or pre-defined algorithms such as counting the number of subsystems or classes and converting them to function points.
- Size-based estimation models
- Parametric models
- Analogy-based estimation
- Statistical sizing - Provides a range of potential sizes that is characterized by least, likely, and most.
- Combination-based estimation: The quantification step is based on a judgmental and mechanical combination of estimates from different sources.
- Mechanical combination - average of an analogy-based and a Work breakdown structure-based
- Judgmental combination - expert judgment from a parametric model and group estimation
References
[1] https://4pm.com/2017/03/01/project-estimation-process-2/
[2] https://www.teamgantt.com/guide-to-project-management/how-to-estimate-projects
[3] http://galorath.com/blog/ten-step-project-estimation-process/
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