Software quality assurance to comply with user requirements enables software development companies to be competitive. Maintaining a high quality level requires continuous monitoring and development. If there are quality problems, the company’s reputation is suffering and its costs increase because of investing in time and eliminating the consequences of the problems. The aim of the present article is to identify the most essential root causes of software defect. The e-service “Invoice Submission” of Riga City Municipality is used as an example. The results of the study can provide useful information for developing improvement activities for e-service higher quality. The analysis is based on the information that is available in the developer’s user request database. The Ishikawa method is used to analyse the causes of defects.
 M. Leszak, D. E. Perry, and D. Stoll, “A Case Study in Root Cause Defect Analysis,” Proceedings of the 22nd international conference on Software engineering - ICSE ’00, pp. 433-434, Jun. 2000. https://doi.org/10.1145/337180.337232
 A. A. Shenvi, “Defect Prevention with Orthogonal Defect Classification,” Proceeding of the 2nd annual conference on India software engineering conference - ISEC ’09, p. 83, 2009. https://doi.org/10.1145/1506216.1506232
 V. Gupta, N. Ganeshan, and T. Singhal Kumar, “Determining the Root Causes of Various Software Bugs Through Software Metrics”, 2015 2nd International Conference on Computing for Sustainable Global Development (INDIACom), 11-13 March, New Delhi, p. 1212, 2015.
 “IEEE Standard Classification for Software Anomalies,” Revision of IEEE Std 1044-2009, p. 8, 2010. https://doi.org/10.1109/ieeestd.2010.5399061
 S. Pertet and P. Narasimhan, Causes of Failure in Web Applications. Parallel Data Laboratory Carnegie Mellon University Pittsburgh, PA 15213-3890, CMU-PDL-05-109, pp. 3-8, Dec. 2005 [Online]. Aviable: http://www.cs.cmu.edu/~priya/PDL-CMU-05-109.pdf
 D. N. Card, “Learning from Our Mistakes with Defect Causal Analysis,” IEEE Software, vol. 15, no. 1, pp. 56-63, 1998. https://doi.org/10.1109/52.646883
 S. Li, H. Zhou, T. Xiao, H. Lin, W. Lin, and T. Xie, “A characteristic study on failures of production distributed data-parallel programms,” Proceeding of the 2013 International Conference on Software Engineering, p. 963-972, 2013. https://dl.acm.org/citation.cfm?id=2486921&CFID=1010944701&CFTOKEN=99591560
 N. Nuzhat, K. Aihab, and K. Ahmed, “Survey to Improve Software Quality Assurance in Developing Countries,” International Journal of Technology and Research, Islamabad 3.1 1-6, pp. 3-5, 2015.
 M. Hamill and K. Goseva-Popstojanova, “Common Trends in Software Fault and Failure Data,” IEEE Transactions on Software Engineering, vol. 35, no. 4, pp. 484-496, Jul. 2009. https://doi.org/10.1109/tse.2009.3
 N. Hrgarek, “Fabasoft Best Practices and Test Metrics Model,” Journal of Information and Organizational Sciences, vol 31, no 1, Austria, pp. 75, 2007 [Online]. Available: http://jios.foi.hr/index.php/jios/article/view/31/29
 “ISTQB Glossary” [Online]. Available: http://glossary.istqb.org/search/defect
 ISTQB, “Why is Testing Necessary,” Certified Tester, Foundation Level Syllabus, p. 11, 2012 [Online]. Available: http://www.istqb.org/downloads/send/2-foundation-level-documents/3- foundation-level-syllabus-2011.html4
 D. Dhandapani, “Applying the Fishbone diageam and Pareto principle to Domino,” 2004 [Online]. Available: https://www.ibm.com/developerworks/lotus/library/fishbone/
 ISTQB, “Types of Process Improvement,” Certified Tester, Advanced Level Syllabus Test Manager, p. 60, 2012 [Online]. Available: http://www.istqb.org/downloads/send/10-advanced-level-syllabus-2012/54-advanced-level-syllabus-2012-test-manager.html