Agreement and Systematic Differences between Analog and Digital Tools for Body Mass Index Assessment in Undergraduate Students in Nigeria

International audience Background: Accurate anthropometric measurement is fundamental for valid Body Mass Index (BMI) classification. In resource-variable settings like Nigeria, both analog and digital tools are used, yet there is a paucity of empirical evidence comparing their accuracy and reliability, particularly among university students.Methods: This cross-sectional comparative study recruited 475 undergraduates (age 18-30 years) using convenience sampling. Height and weight were measured using calibrated analog (SECA mechanical scale and stadiometer) and an integrated AI-Enhanced Smart Digital standalone BMI machine designed and developed by the authors. Descriptive statistics, paired-sample t-tests, Pearson’s correlation, and Cronbach’s alpha were used for analysis.Results: Analog devices recorded a significantly greater mean height (169.16 ± 7.85 cm) than digital devices (167.43 ± 8.34 cm). Conversely, digital devices yielded significantly higher mean weight (64.82 ± 13.98 vs. 63.89 ± 14.01 kg) and BMI (23.12 ± 4.70 vs. 22.25 ± 4.36 kg/m²) (p < 0.001 for all comparisons). Despite these systematic differences, a very strong positive correlation (r = 0.94) and excellent reliability (Cronbach’s α = 0.97) were observed between the devices.Conclusion: While both device types are highly reliable and yield strongly correlated values, they produce statistically significant systematic differences in measurements. Therefore, analog and digital tools should not be used interchangeably for clinical or research purposes without adjustment, as the observed systematic differences in measurements could lead to BMI misclassification, affect the accuracy of population health screening, and undermine the standardization of research data. Digital devices are recommended for enhanced precision, whereas analog tools remain viable in low-resource settings provided rigorous calibration and standardized protocols are maintained.