| 1. |
- Angelis, Lefteris, et al.
(författare)
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A Framework of Statistical and Visualization Techniques for Missing Data Analysis in Software Cost Estimation
- 2018
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Ingår i: Computer Systems and Software Engineering. - : IGI Global. - 9781522539230 - 9781522539247 ; , s. 433-460
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Software Cost Estimation (SCE) is a critical phase in software development projects. However, due to the growing complexity of the software itself, a common problem in building software cost models is that the available datasets contain lots of missing categorical data. The purpose of this chapter is to show how a framework of statistical, computational, and visualization techniques can be used to evaluate and compare the effect of missing data techniques on the accuracy of cost estimation models. Hence, the authors use five missing data techniques: Multinomial Logistic Regression, Listwise Deletion, Mean Imputation, Expectation Maximization, and Regression Imputation. The evaluation and the comparisons are conducted using Regression Error Characteristic curves, which provide visual comparison of different prediction models, and Regression Error Operating Curves, which examine predictive power of models with respect to under- or over-estimation.
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| 2. |
- Angelis, Lefteris, et al.
(författare)
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Methods for Statistical and Visual Comparison of Imputation Methods for Missing Data in Software Cost Estimation
- 2011
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Ingår i: Modern Software Engineering Concepts and Practices. - : IGI Global. - 9781609602154 - 9781609602178 ; , s. 221-241
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Bokkapitel (refereegranskat)abstract
- Software Cost Estimation is a critical phase in the development of a software project, and over the years has become an emerging research area. A common problem in building software cost models is that the available datasets contain projects with lots of missing categorical data. The purpose of this chapter is to show how a combination of modern statistical and computational techniques can be used to compare the effect of missing data techniques on the accuracy of cost estimation. Specifically, a recently proposed missing data technique, the multinomial logistic regression, is evaluated and compared with four older methods: listwise deletion, mean imputation, expectation maximization and regression imputation with respect to their effect on the prediction accuracy of a least squares regression cost model. The evaluation is based on various expressions of the prediction error and the comparisons are conducted using statistical tests, resampling techniques and a visualization tool, the regression error characteristic curves.
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| 3. |
- Azhar, Damir, et al.
(författare)
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Using ensembles for web effort estimation
- 2013
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Konferensbidrag (refereegranskat)abstract
- Background: Despite the number of Web effort estimation techniques investigated, there is no consensus as to which technique produces the most accurate estimates, an issue shared by effort estimation in the general software estimation domain. A previous study in this domain has shown that using ensembles of estimation techniques can be used to address this issue. Aim: The aim of this paper is to investigate whether ensembles of effort estimation techniques will be similarly successful when used on Web project data. Method: The previous study built ensembles using solo effort estimation techniques that were deemed superior. In order to identify these superior techniques two approaches were investigated: The first involved replicating the methodology used in the previous study, while the second approach used the Scott-Knott algorithm. Both approaches were done using the same 90 solo estimation techniques on Web project data from the Tukutuku dataset. The replication identified 16 solo techniques that were deemed superior and were used to build 15 ensembles, while the Scott-Knott algorithm identified 19 superior solo techniques that were used to build two ensembles. Results: The ensembles produced by both approaches performed very well against solo effort estimation techniques. With the replication, the top 12 techniques were all ensembles, with the remaining 3 ensembles falling within the top 17 techniques. These 15 effort estimation ensembles, along with the 2 built by the second approach, were grouped into the best cluster of effort estimation techniques by the Scott-Knott algorithm. Conclusion: While it may not be possible to identify a single best technique, the results suggest that ensembles of estimation techniques consistently perform well even when using Web project data
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| 4. |
- Baliakas, Panagiotis, et al.
(författare)
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Clinical effect of stereotyped B-cell receptor immunoglobulins in chronic lymphocytic leukaemia: a retrospective multicentre study
- 2014
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Ingår i: The Lancet Haematology. - 2352-3026. ; 1:2, s. 74-84
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Tidskriftsartikel (refereegranskat)abstract
- Background About 30% of cases of chronic lymphocytic leukaemia (CLL) carry quasi-identical B-cell receptor immunoglobulins and can be assigned to distinct stereotyped subsets. Although preliminary evidence suggests that B-cell receptor immunoglobulin stereotypy is relevant from a clinical viewpoint, this aspect has never been explored in a systematic manner or in a cohort of adequate size that would enable clinical conclusions to be drawn. Methods For this retrospective, multicentre study, we analysed 8593 patients with CLL for whom immunogenetic data were available. These patients were followed up in 15 academic institutions throughout Europe (in Czech Republic, Denmark, France, Greece, Italy, Netherlands, Sweden, and the UK) and the USA, and data were collected between June 1, 2012, and June 7, 2013. We retrospectively assessed the clinical implications of CLL B-cell receptor immunoglobulin stereotypy, with a particular focus on 14 major stereotyped subsets comprising cases expressing unmutated (U-CLL) or mutated (M-CLL) immunoglobulin heavy chain variable genes. The primary outcome of our analysis was time to first treatment, defined as the time between diagnosis and date of first treatment. Findings 2878 patients were assigned to a stereotyped subset, of which 1122 patients belonged to one of 14 major subsets. Stereotyped subsets showed significant differences in terms of age, sex, disease burden at diagnosis, CD38 expression, and cytogenetic aberrations of prognostic significance. Patients within a specific subset generally followed the same clinical course, whereas patients in different stereotyped subsets-despite having the same immunoglobulin heavy variable gene and displaying similar immunoglobulin mutational status-showed substantially different times to first treatment. By integrating B-cell receptor immunoglobulin stereotypy (for subsets 1, 2, and 4) into the well established Dohner cytogenetic prognostic model, we showed these, which collectively account for around 7% of all cases of CLL and represent both U-CLL and M-CLL, constituted separate clinical entities, ranging from very indolent (subset 4) to aggressive disease (subsets 1 and 2). Interpretation The molecular classification of chronic lymphocytic leukaemia based on B-cell receptor immunoglobulin stereotypy improves the Dohner hierarchical model and refines prognostication beyond immunoglobulin mutational status, with potential implications for clinical decision making, especially within prospective clinical trials.
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| 5. |
- Baliakas, Panagiotis, et al.
(författare)
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Not all IGHV3-21 chronic lymphocytic leukemias are equal: prognostic considerations.
- 2015
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Ingår i: Blood. - : American Society of Hematology. - 1528-0020 .- 0006-4971. ; 125:5, s. 856-859
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Tidskriftsartikel (refereegranskat)abstract
- An unresolved issue in chronic lymphocytic leukemia (CLL) is whether IGHV3-21 gene usage, in general, or the expression of stereotyped B-cell receptor immunoglobulin defining subset #2 (IGHV3-21/IGLV3-21), in particular, determines outcome for IGHV3-21-utilizing cases. We reappraised this issue in 8593 CLL patients of whom 437 (5%) used the IGHV3-21 gene with 254/437 (58%) classified as subset #2. Within subset #2, immunoglobulin heavy variable (IGHV)-mutated cases predominated, whereas non-subset #2/IGHV3-21 was enriched for IGHV-unmutated cases (P = .002). Subset #2 exhibited significantly shorter time-to-first-treatment (TTFT) compared with non-subset #2/IGHV3-21 (22 vs 60 months, P = .001). No such difference was observed between non-subset #2/IGHV3-21 vs the remaining CLL with similar IGHV mutational status. In conclusion, IGHV3-21 CLL should not be axiomatically considered a homogeneous entity with adverse prognosis, given that only subset #2 emerges as uniformly aggressive, contrasting non-subset #2/IGVH3-21 patients whose prognosis depends on IGHV mutational status as the remaining CLL.
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| 6. |
- Barney, Sebastian, et al.
(författare)
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Offshore insourcing : A case study on software quality alignment
- 2011
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Ingår i: 2011 IEEE Sixth International Conference on Global Software Engineering. - Helsinki : IEEE. - 9781457711404 - 9780769545035 ; , s. 146-155
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Konferensbidrag (refereegranskat)abstract
- Background: Software quality issues are commonly reported when off shoring software development. Value-based software engineering addresses this by ensuring key stakeholders have a common understanding of quality. Aim: This work seeks to understand the levels of alignment between key stakeholders on aspects of software quality for two products developed as part of an offshore in sourcing arrangement. The study further aims to explain the levels of alignment identified. Method: Representatives of key stakeholder groups for both products ranked aspects of software quality. The results were discussed with the groups to gain a deeper understanding. Results: Low levels of alignment were found between the groups studied. This is associated with insufficiently defined quality requirements, a culture that does not question management and conflicting temporal reflections on the product's quality. Conclusion: The work emphasizes the need for greater support to align success-critical stakeholder groups in their understanding of quality when off shoring software development
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| 7. |
- Barney, Sebastian, et al.
(författare)
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Software quality across borders : Three case studies on company internal alignment
- 2014
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Ingår i: Information and Software Technology. - : Elsevier. - 0950-5849 .- 1873-6025. ; 56:1, s. 20-38
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Tidskriftsartikel (refereegranskat)abstract
- Context: Software quality issues are commonly reported when offshoring software development. Value-based software engineering addresses this by ensuring key stakeholders have a common understanding of quality.Objective: This work seeks to understand the levels of alignment between key stakeholder groups within a company on the priority given to aspects of software quality developed as part of an offshoring relationship. Furthermore, the study aims to identify factors impacting the levels of alignment identified.Method: Three case studies were conducted, with representatives of key stakeholder groups ranking aspects of software quality in a hierarchical cumulative exercise. The results are analysed using Spearman rank correlation coefficients and inertia. The results were discussed with the groups to gain a deeper understanding of the issues impacting alignment.Results: Various levels of alignment were found between the various groups. The reasons for misalignment were found to include cultural factors, control of quality in the development process, short-term versus long-term orientations, understanding of cost-benefits of quality improvements, communication and coordination.Conclusions: The factors that negatively affect alignment can vary greatly between different cases. The work emphasises the need for greater support to align company internal success-critical stakeholder groups in their understanding of quality when offshoring software development.
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| 8. |
- Chatzipetrou, Panagiota, Assistant Professor, 1984-, et al.
(författare)
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A multivariate statistical framework for the analysis of software effort phase distribution
- 2015
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Ingår i: Information and Software Technology. - : Elsevier. - 0950-5849 .- 1873-6025. ; 59, s. 149-169
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Tidskriftsartikel (refereegranskat)abstract
- Context: In software project management, the distribution of resources to various project activities is one of the most challenging problems since it affects team productivity, product quality and project constraints related to budget and scheduling.Objective: The study aims to (a) reveal the high complexity of modelling the effort usage proportion in different phases as well as the divergence from various rules-of-thumb in related literature, and (b) present a systematic data analysis framework, able to offer better interpretations and visualisation of the effort distributed in specific phases.Method: The basis for the proposed multivariate statistical framework is Compositional Data Analysis, a methodology appropriate for proportions, along with other methods like the deviation from rules-ofthumb, the cluster analysis and the analysis of variance. The effort allocations to phases, as reported in around 1500 software projects of the ISBSG R11 repository, were transformed to vectors of proportions of the total effort and were analysed with respect to prime project attributes.Results: The proposed statistical framework was able to detect high dispersion among data, distribution inequality and various interesting correlations and trends, groupings and outliers, especially with respect to other categorical and continuous project attributes. Only a very small number of projects were found close to the rules-of-thumb from the related literature. Significant differences in the proportion of effort spent in different phrases for different types of projects were found.Conclusion: There is no simple model for the effort allocated to phases of software projects. The data from previous projects can provide valuable information regarding the distribution of the effort for various types of projects, through analysis with multivariate statistical methodologies. The proposed statistical framework is generic and can be easily applied in a similar sense to any dataset containing effort allocation to phases.
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| 9. |
- Chatzipetrou, Panagiota, Assistant Professor, 1984-, et al.
(författare)
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An experience-based framework for evaluating alignment of software quality goals
- 2015
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Ingår i: Software quality journal. - : Springer. - 0963-9314 .- 1573-1367. ; 23:4, s. 567-594
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Tidskriftsartikel (refereegranskat)abstract
- Efficient quality management of software projects requires knowledge of how various groups of stakeholders involved in software development prioritize the product and project goals. Agreements or disagreements among members of a team may originate from inherent groupings, depending on various professional or other characteristics. These agreements are not easily detected by conventional practices (discussions, meetings, etc.) since the natural language expressions are often obscuring, subjective, and prone to misunderstandings. It is therefore essential to have objective tools that can measure the alignment among the members of a team; especially critical for the software development is the degree of alignment with respect to the prioritization goals of the software product. The paper proposes an experience-based framework of statistical and graphical techniques for the systematic study of prioritization alignment, such as hierarchical cluster analysis, analysis of cluster composition, correlation analysis, and closest agreement-directed graph. This framework can provide a thorough and global picture of a team's prioritization perspective and can potentially aid managerial decisions regarding team composition and leadership. The framework is applied and illustrated in a study related to global software development where 65 individuals in different roles, geographic locations and professional relationships with a company, prioritize 24 goals from individual perception of the actual situation and for an ideal situation.
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| 10. |
- Chatzipetrou, Panagiota, Assistant Professor, 1984-, et al.
(författare)
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An Investigation of Software Effort Phase Distribution Using Compositional Data Analysis
- 2012
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Ingår i: 38th EUROMICRO Conference on Software Engineering and Advanced Applications, SEAA 2012. - : IEEE. - 9780769547909 ; , s. 367-375
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Konferensbidrag (refereegranskat)abstract
- One of the most significant problems faced by project managers is to effectively distribute the project resources and effort among the various project activities. Most importantly, project success depends on how well, or how balanced, the work effort is distributed among the project phases. This paper aims to obtain useful information regarding the correlation of the composition of effort attributed in phases for around 1,500 software projects of the ISBSG R11 database based on a promising statistical method called Compositional Data Analysis (CoDA). The motivation for applying this analysis is the observation that certain types of project data (effort distributions and attributes) do not relate in a direct way but present a spurious correlation. Effort distribution is compared to the project life-cycle activities, organization type, language type, function points and other prime project attributes. The findings are beneficial for building a basis for software cost estimation and improving future empirical software studies.
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