Assessment of Laboratory Performance Evaluation in Determining Al, Fe, and N Content on Some Soil Samples Based on Soil Analytical Method using Youden Plot and Ranking Test
An attempt is made in this work to compare the quality of laboratories with regard to their analytical results and also the comparison of the quality of methods of analysis with regard to their sensitivity to various soil samples analyzed during an IAEA-WEPAL organized proficiency test in 2010 which Nigeria is a signatory to. The methods used for the comparison include: the Youden plot and the ranking test. These statistical methods were used to analyze the results obtained from participant laboratories in which the determination of the content of Al, Fe, and N on four soil samples namely Braunerde Clay (ID 872), Sandy Soil (ID 995), Clay (ID 883) and Sandy-Clay Soil (ID 958) were considered due to the fact that most of the participant laboratories on the program determined the three elements under consideration. 26 laboratories results were analyzed for Al, 25 for Fe and a total of 8 analytical methods for both the two. Based on the results obtained from Youden plot and Ranking Test, the 7 labs with codes 14, 42, 64, 92, 95, 149 and 160 have most accurate and precise results. For N, 40 analytical labs were assessed and out of that, 7 labs with codes 24, 29, 63, 134, 238, 275 and 295 have the most precise results. Those that have outlying value has also been grouped under two types of errors namely, the systematic and the random errors. We also observed that the quality of results from a laboratory depends on its analytical techniques, thus we were able to statistically group and differentiate results from laboratories based on their performances with respect to their analytical methods. We identified the areas of deficiencies of the laboratories by checking whether the errors are from the laboratory or from the methods used. The work was able to demonstrate that the quality of laboratories cannot be equivalent even when the laboratories used the same analytical method. We therefore recommend these laboratories that have the precise and accurate values as the best laboratories to be consulted while determining the content of Al, Fe and N on soil samples. We also recommend the best methods for the determinations.