Data for the determination of elements in clay samples both by neutron activation (NAA) and x-ray fluorescence (XRF) analysis were analyzed statistically in order to decide on the method to be used in future work. The groups obtained by using the concentration of elements determined by NAA agree very well with the groups obtained with the XRF analysis data. The groups obtained from NAA data are more compact (fewer outliers) than those from XRF analysis data. The reason for this is the larger number of elements determined by NAA, which makes the constituents of a group less sensitive to the variation of error in the determination of a particular element. -- AATA