PROxy Based Estimating (PROBE)

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PROxy Based Estimating (PROBE) is a technique used in software development for estimating the size, effort, and duration of a project based on historical data and the use of proxies. Proxies are measurable attributes or characteristics of a software system that can be used to estimate its size or complexity. PROBE is a part of the Personal Software Process (PSP), developed by Watts Humphrey, which is a methodology aimed at helping individual software developers improve their personal productivity and software quality.

Purpose and Role

The purpose of PROBE is to provide a structured and data-driven approach for estimating software projects, ultimately leading to more accurate and reliable estimates. The role of PROBE includes:

  • Estimating project size: By using proxies, developers can estimate the size of a project in terms of lines of code, function points, or other relevant metrics.
  • Estimating effort: Based on historical data and the size estimate, developers can predict the amount of effort required to complete the project.
  • Estimating duration: Using the effort estimate and available resources, developers can estimate the duration or schedule of the project.


PROBE consists of several components, which together form the basis of the estimation process:

  • Historical data: PROBE relies on historical data from previous projects to provide a basis for estimation. Developers should maintain a database of their past projects, including size, effort, and duration metrics.
  • Proxy: A proxy is a measurable attribute or characteristic of a software system that can be used to estimate its size or complexity. Examples of proxies include lines of code, function points, and object points.
  • Estimation equations: PROBE uses estimation equations based on linear regression or other statistical methods to relate proxies to effort and duration. Developers can derive these equations from their historical data.
  • Prediction: Using the proxy values and estimation equations, developers can predict the size, effort, and duration of a new project.


PROBE is important in software development for several reasons:

  • Data-driven approach: PROBE uses historical data and statistical methods to produce more accurate and reliable estimates, reducing the risk of over- or under-estimating project resources and timelines.
  • Personalized estimation: PROBE allows developers to create personalized estimation models based on their own historical data, taking into account individual differences in productivity and experience.
  • Continuous improvement: By maintaining a database of historical project data, developers can continually refine and improve their estimation models, leading to better predictions over time.


Suppose a software developer has historical data for three previous projects:

  • Project A: 2,000 lines of code, 150 hours of effort, 4 weeks duration.
  • Project B: 4,500 lines of code, 300 hours of effort, 8 weeks duration.
  • Project C: 6,000 lines of code, 450 hours of effort, 10 weeks duration.

The developer can use this data to create a linear regression model relating lines of code (proxy) to effort and duration. For a new project with an estimated 3,000 lines of code, the developer can then use the regression model to predict the effort and duration required to complete the project.

See Also

Software Development