Software development effort estimation

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In software development, effort estimation 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. Effort estimates may be used as input to project plans, iteration plans, budgets, investment analyses, pricing processes and bidding rounds. [1] [2]

Contents

State-of-practice

Published surveys on estimation practice suggest that expert estimation is the dominant strategy when estimating software development effort. [3]

Typically, effort estimates are over-optimistic and there is a strong over-confidence in their accuracy. The mean effort overrun seems to be about 30% and not decreasing over time. For a review of effort estimation error surveys, see. [4] However, the measurement of estimation error is problematic, see Assessing the accuracy of estimates. The strong overconfidence in the accuracy of the effort estimates is illustrated by the finding that, on average, if a software professional is 90% confident or "almost sure" to include the actual effort in a minimum-maximum interval, the observed frequency of including the actual effort is only 60-70%. [5]

Currently the term "effort estimate" is used to denote as different concepts such as most likely use of effort (modal value), the effort that corresponds to a probability of 50% of not exceeding (median), the planned effort, the budgeted effort or the effort used to propose a bid or price to the client. This is believed to be unfortunate, because communication problems may occur and because the concepts serve different goals. [6] [7]

History

Software researchers and practitioners have been addressing the problems of effort estimation for software development projects since at least the 1960s; see, e.g., work by Farr [8] [9] and Nelson. [10]

Most of the research has focused on the construction of formal software effort estimation models. The early models were typically based on regression analysis or mathematically derived from theories from other domains. Since then a high number of model building approaches have been evaluated, such as approaches founded on case-based reasoning, classification and regression trees, simulation, neural networks, Bayesian statistics, lexical analysis of requirement specifications, genetic programming, linear programming, economic production models, soft computing, fuzzy logic modeling, statistical bootstrapping, and combinations of two or more of these models. The perhaps most common estimation methods today are the parametric estimation models COCOMO, SEER-SEM and SLIM. They have their basis in estimation research conducted in the 1970s and 1980s and are since then updated with new calibration data, with the last major release being COCOMO II in the year 2000. The estimation approaches based on functionality-based size measures, e.g., function points, is also based on research conducted in the 1970s and 1980s, but are re-calibrated with modified size measures and different counting approaches, such as the use case points [11] or object points and COSMIC Function Points in the 1990s.

Estimation approaches

There are many ways of categorizing estimation approaches, see for example. [12] [13] The top level categories are the following:

Below are examples of estimation approaches within each category.

Estimation approachCategoryExamples of support of implementation of estimation approach
Analogy-based estimationFormal estimation modelANGEL, Weighted Micro Function Points
WBS-based (bottom up) estimationExpert estimation Project management software, company specific activity templates
Parametric modelsFormal estimation model COCOMO, SLIM, SEER-SEM, TruePlanning for Software
Size-based estimation models [15] Formal estimation model Function Point Analysis, [16] Use Case Analysis, Use Case Points, SSU (Software Size Unit), Story points-based estimation in Agile software development, Object Points
Group estimationExpert estimation Planning poker, Wideband delphi
Mechanical combinationCombination-based estimationAverage of an analogy-based and a Work breakdown structure-based effort estimate [17]
Judgmental combinationCombination-based estimationExpert judgment based on estimates from a parametric model and group estimation

Selection of estimation approaches

The evidence on differences in estimation accuracy of different estimation approaches and models suggest that there is no "best approach" and that the relative accuracy of one approach or model in comparison to another depends strongly on the context . [18] This implies that different organizations benefit from different estimation approaches. Findings [19] that may support the selection of estimation approach based on the expected accuracy of an approach include:

The most robust finding, in many forecasting domains, is that combination of estimates from independent sources, preferable applying different approaches, will on average improve the estimation accuracy. [19] [20] [21]

It is important to be aware of the limitations of each traditional approach to measuring software development productivity. [22]

In addition, other factors such as ease of understanding and communicating the results of an approach, ease of use of an approach, and cost of introduction of an approach should be considered in a selection process.

Assessing the accuracy of estimates

The most common measure of the average estimation accuracy is the MMRE (Mean Magnitude of Relative Error), where the MRE of each estimate is defined as:

MRE = |(actual effort) - (estimated effort)|/(actual effort)

This measure has been criticized [23] [24] [25] and there are several alternative measures, such as more symmetric measures, [26] Weighted Mean of Quartiles of relative errors (WMQ) [27] and Mean Variation from Estimate (MVFE). [28]

MRE is not reliable if the individual items are skewed. PRED(25) is preferred as a measure of estimation accuracy. PRED(25) measures the percentage of predicted values that are within 25 percent of the actual value.

A high estimation error cannot automatically be interpreted as an indicator of low estimation ability. Alternative, competing or complementing, reasons include low cost control of project, high complexity of development work, and more delivered functionality than originally estimated. A framework for improved use and interpretation of estimation error measurement is included in. [29]

Psychological issues

There are many psychological factors potentially explaining the strong tendency towards over-optimistic effort estimates. These factors are essential to consider even when using formal estimation models, because much of the input to these models is judgment-based. Factors that have been demonstrated to be important are wishful thinking, anchoring, planning fallacy and cognitive dissonance. [30]

Humor

The chronic underestimation of development effort has led to the coinage and popularity of numerous humorous adages, such as ironically referring to a task as a "small matter of programming" (when much effort is likely required), and citing laws about underestimation:

The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time. [31]

— Tom Cargill, Bell Labs

Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

—  Douglas Hofstadter, Gödel, Escher, Bach: An Eternal Golden Braid [32]

What one programmer can do in one month, two programmers can do in two months.

—  Fred Brooks

Comparison of development estimation software

SoftwareSchedule estimateCost estimateCost ModelsInputReport Output Format Supported Programming Languages Platforms Cost License
AFCAA REVIC [33] YesYesREVIC KLOC, Scale Factors, Cost Driversproprietary, TextAnyDOSFreeProprietary
/ Free for public distribution
Seer for Software YesYes SEER-SEM SLOC, Function points, use cases, bottoms-up, object, featuresproprietary, Excel, Microsoft Project, IBM Rational, Oracle Crystal BallAnyWindows, Any (Web-based)Commercial Proprietary
SLIM [34] YesYes SLIM Size (SLOC, Function points, Use Cases, etc.), constraints (size, duration, effort, staff), scale factors, historical projects, historical trendsproprietary, Excel, Microsoft Project, Microsoft PowerPoint, IBM Rational, text, HTMLAnyWindows, Any (Web-based) [35] Commercial Proprietary
TruePlanning [36] YesYesPRICEComponents, Structures, Activities, Cost drivers, Processes, Functional Software Size (Source Lines of Code (SLOC), Function Points, Use Case Conversion Points (UCCP), Predictive Object Points (POPs) etc.)Excel, CADAnyWindowsCommercial Proprietary

See also

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References

  1. ↑ "What We do and Don't Know about Software Development Effort Estimation".
  2. ↑ "Cost Estimating And Assessment Guide GAO-09-3SP Best Practices for developing and managing Capital Program Costs" (PDF). US Government Accountability Office. 2009.
  3. ↑ Jørgensen, M. (2004). "A Review of Studies on Expert Estimation of Software Development Effort". Journal of Systems and Software. 70 (1–2): 37–60. doi:10.1016/S0164-1212(02)00156-5.
  4. ↑ Molokken, K. Jorgensen, M. (2003). "A review of software surveys on software effort estimation". 2003 International Symposium on Empirical Software Engineering, 2003. ISESE 2003. Proceedings. pp. 223–230. doi:10.1109/ISESE.2003.1237981. ISBN   978-0-7695-2002-5. S2CID   15471986.{{cite book}}: CS1 maint: multiple names: authors list (link)
  5. ↑ Jørgensen, M. Teigen, K.H. Ribu, K. (2004). "Better sure than safe? Over-confidence in judgement based software development effort prediction intervals". Journal of Systems and Software. 70 (1–2): 79–93. doi:10.1016/S0164-1212(02)00160-7.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ↑ Edwards, J.S. Moores (1994). "A conflict between the use of estimating and planning tools in the management of information systems". European Journal of Information Systems . 3 (2): 139–147. doi:10.1057/ejis.1994.14. S2CID   62582672.
  7. ↑ Goodwin, P. (1998). Enhancing judgmental sales forecasting: The role of laboratory research. Forecasting with judgment. G. Wright and P. Goodwin. New York, John Wiley & Sons: 91-112. Hi
  8. ↑ Farr, L. Nanus, B. "Factors that affect the cost of computer programming, volume I" (PDF). Archived from the original (PDF) on February 21, 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
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  10. ↑ Nelson, E. A. (1966). Management Handbook for the Estimation of Computer Programming Costs. AD-A648750, Systems Development Corp.
  11. ↑ Anda, B. Angelvik, E. Ribu, K. (2002). "Improving Estimation Practices by Applying Use Case Models". Product Focused Software Process Improvement. Lecture Notes in Computer Science. Vol. 2559. pp. 383–397. CiteSeerX   10.1.1.546.112 . doi:10.1007/3-540-36209-6_32. ISBN   978-3-540-00234-5.{{cite book}}: CS1 maint: multiple names: authors list (link) ISBN   9783540002345 , 9783540362098.
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  13. ↑ Jørgensen, M. Shepperd, M. "A Systematic Review of Software Development Cost Estimation Studies".{{cite web}}: CS1 maint: multiple names: authors list (link)
  14. ↑ "Custom Software Development Services – Custom App Development – Oxagile".
  15. ↑ Hill Peter (ISBSG) – Estimation Workbook 2 – published by International Software Benchmarking Standards Group ISBSG - Estimation and Benchmarking Resource Centre Archived 2008-08-29 at the Wayback Machine
  16. ↑ Morris Pam — Overview of Function Point Analysis Total Metrics - Function Point Resource Centre
  17. ↑ Srinivasa Gopal and Meenakshi D'Souza. 2012. Improving estimation accuracy by using case based reasoning and a combined estimation approach. In Proceedings of the 5th India Software Engineering Conference (ISEC '12). ACM, New York, USA, 75-78. doi : 10.1145/2134254.2134267
  18. ↑ Shepperd, M. Kadoda, G. (2001). "Comparing software prediction techniques using simulation". IEEE Transactions on Software Engineering. 27 (11): 1014–1022. doi:10.1109/32.965341.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. 1 2 Jørgensen, M. "Estimation of Software Development Work Effort:Evidence on Expert Judgment and Formal Models".
  20. ↑ Winkler, R.L. (1989). "Combining forecasts: A philosophical basis and some current issues Manager". International Journal of Forecasting. 5 (4): 605–609. doi:10.1016/0169-2070(89)90018-6.
  21. ↑ Blattberg, R.C. Hoch, S.J. (1990). "Database Models and Managerial Intuition: 50% Model + 50% Manager". Management Science. 36 (8): 887–899. doi:10.1287/mnsc.36.8.887. JSTOR   2632364.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  22. ↑ BlueOptima (2019-10-29). "Identifying Reliable, Objective Software Development Metrics".
  23. ↑ Shepperd, M. Cartwright, M. Kadoda, G. (2000). "On Building Prediction Systems for Software Engineers". Empirical Software Engineering. 5 (3): 175–182. doi:10.1023/A:1026582314146. S2CID   1293988.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  24. ↑ Kitchenham, B., Pickard, L.M., MacDonell, S.G. Shepperd. "What accuracy statistics really measure".{{cite web}}: CS1 maint: multiple names: authors list (link)
  25. ↑ Foss, T., Stensrud, E., Kitchenham, B., Myrtveit, I. (2003). "A Simulation Study of the Model Evaluation Criterion MMRE". IEEE Transactions on Software Engineering. 29 (11): 985–995. CiteSeerX   10.1.1.101.5792 . doi:10.1109/TSE.2003.1245300.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  26. ↑ Miyazaki, Y. Terakado, M. Ozaki, K. Nozaki, H. (1994). "Robust regression for developing software estimation models". Journal of Systems and Software. 27: 3–16. doi:10.1016/0164-1212(94)90110-4.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ↑ Lo, B. Gao, X. "Assessing Software Cost Estimation Models: criteria for accuracy, consistency and regression".{{cite web}}: CS1 maint: multiple names: authors list (link)
  28. ↑ Hughes, R.T. Cunliffe, A. Young-Martos, F. (1998). "Evaluating software development effort model-building techniquesfor application in a real-time telecommunications environment". IEE Proceedings - Software. 145: 29. doi:10.1049/ip-sen:19983370.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  29. ↑ Grimstad, S. Jørgensen, M. (2006). "A Framework for the Analysis of Software Cost Estimation Accuracy".{{cite web}}: CS1 maint: multiple names: authors list (link)
  30. ↑ Jørgensen, M. Grimstad, S. (2008). "How to Avoid Impact from Irrelevant and Misleading Information When Estimating Software Development Effort". IEEE Software: 78–83.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  31. ↑ Bentley, Jon (1985). "Programming pearls" (fee required). Communications of the ACM. 28 (9): 896–901. doi: 10.1145/4284.315122 . ISSN   0001-0782. S2CID   5832776.
  32. ↑ Gödel, Escher, Bach: An Eternal Golden Braid. 20th anniversary ed., 1999, p. 152. ISBN   0-465-02656-7.
  33. ↑ AFCAA Revic 9.2 manual Revic memorial site
  34. ↑ "SLIM Suite Overview". Qsm.com. Retrieved 2019-08-27.
  35. ↑ "SLIM-WebServices". Qsm.com. Retrieved 2019-08-27.
  36. ↑ TruePlanning Integrated Cost Models PRICE Systems site Archived 2015-11-05 at the Wayback Machine
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