Investigating the Impact of Structured Code Review on Software Defect Rates in Nigerian Software Companies

Code review is a well-established defect prevention practice in software engineering, yet its systematic adoption and impact in Nigerian software companies has not been empirically investigated. This study examines the relationship between structured code review practices and software defect rates across 10 Nigerian software companies in Lagos and Abuja, spanning fintech, health technology, and enterprise software sectors. A retrospective analysis of 1,800 pull requests and associated defect reports over 12 months provides the quantitative dataset, supplemented by semi-structured interviews with 30 software engineers and team leads. Defect density, pre-release defect detection rate, and post-release defect frequency are computed for projects with and without structured code review protocols. Statistical analysis using Mann-Whitney U tests reveals that projects with structured code review achieve a 41 percent lower post-release defect frequency (p = 0.007) and a 53 percent higher pre-release defect detection rate. Qualitative findings identify reviewer experience, review comment quality standards, and time allocation as the three most influential moderators of code review effectiveness. The study finds that informal or cursory reviews provide negligible defect reduction compared to structured checklist-based reviews. Recommendations include adopting pull request templates with defect-category checklists and enforcing minimum review comment standards. Keywords: code review, software defects, Nigeria, software quality, defect prevention