Abstract: Objective To study a new statistical method for the data of external quality assessment in quantitative determination items. Methods The results of Ministry of Health National Center for Clinical Laboratory external quality assessment for routine chemistry items 2011 were collected. The data were analyzed by a new statistical method. The standard deviation, the traditional Z-score and robust Z-score were added, and the relative difference with the median was added and expressed as the percentage of the allowed difference. The multiple results were plotted on a standardized chart. Results The traditional and robust Z-scores can reflect the consistency of results. The percentage of relative difference D% was used to replace the existing deviation (D%) or bias (%). In addition, it is helpful to compare directly by plotting multiple results in one chart, demonstrating the comparability for each external quality assessment result in the standardization way. Conclusions It is more scientific and appropriate to use the new statistical method for the data of external quality assessment, as it is also helpful for the external quality assessment and continual quality improvement in participating laboratories.

Key words: External quality assessment, Z-score, Routine chemistry