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Background : Weight measurement is part of the care in a pediatric clinic for many reasons. It is important in drug dosing, and nutritional assessment. Error in measuring weight can lead to erroneous clinical care. This study aimed to assess the accuracy of pediatric weighing scales which were in use by the health institutions in Addis Ababa.
Methods : One hundred sixty-seven weighing scales from 70 health institutions were included in the study. Data were collected in May and June 2016. The data collector was a certified person by the National Metrology Institute of Ethiopia on scale assessment and weight calibration. Nationally certified International Organization of Legal Metrology CLASS M1 1 kg, 5 kg, 10 kg and 15 kg standard weights were used to assess the precision and accuracy of the weighing scales. Data were analyzed using Statistical Package for Social Sciences (SPSS) version 21.0 for windows. Wilcoxon Signed Rank test was used to compare the mean differences between initial and final measurements of the weighing scales and to assess the mean difference between the displayed weight and actual weights of the calibration weights. Chi-square test was used to assess factors which could lead to inaccuracy or imprecision of the weighing scales. Statistical significance was considered when the p-value was less than 0.05.

Result : A total of 167 weighing scales were evaluated during the study period. Of the total weighing scales 87(52.1%), 55(32.9%), 43(25.7%), and 25(15.0%) of the scales weighed the 1kg, 5kg, 10 and 15kg standard loads, respectively, accurately. The median of the difference of each scale compared to the weight of the respected standard load of 1kg, 5kg, 10kg and 15kg was 0.0kg (IQR=0.0,0.1), 0.1kg (IQR=0.0,0.2), 1.0kg (IQR=0.0,1.0) and 0.4kg(IQR=0.1,0.6) respectively. Wilcoxon Signed Rank test showed no statistically significant difference between the mean weights of the 10kg standard load which was weighed twice using each weighing scale (p=o.971) indicating the weighing scales were precise.
Conclusion: Our finding showed that the weight scales were precise but not accurate. It emphasizes the need for regular recalibration to obtain accurate measurements.
Keyword: Accuracy, Calibration, weighing scale, pediatrics

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