Assessing the Reliability of Manual Defect Inspection in Bottle Water Production: An Emperical Study from Gombe State, Nigeria

Quality control in manufacturing depends on consistent defect identification, yet inspector variability remains a critical challenge. This study evaluated inter-rater reliability among quality control inspectors at Atlantis Table Water bottling company in Gombe State, Nigeria, examining the interplay of experience, environmental factors, and standardized protocols. Using a stratified sample of 30 inspectors drawn from beginner, intermediate, and experienced levels across three shift schedules, data were collected through structured observations under controlled conditions. Descriptive statistics, Cohen's kappa (κ), two-way ANOVA, and Pearson correlation analyses were employed. Results showed that experienced inspectors achieved 85% mean defect identification accuracy with substantial inter-rater agreement (κ = 0.75), while beginners showed 60% accuracy with fair agreement (κ = 0.35). Environmental factors, particularly poor lighting, reduced defect detection by 15% (p < 0.001). A strong positive correlation was found between experience and accuracy (r = 0.72, p < 0.001). The study concludes that experience and optimized working conditions enhance inspector consistency. Recommendations include structured training programs, standardized lighting (>500 lux), reduced ambient noise (<55 dB), and regular inter-rater reliability assessments.