Importance of skewness and kurtosis statistical tests for outlier detection and elimination in evaluation of geochemical reference materials

Abstract

A common characteristic of concentration data compilations for geochemical reference materials (GRM) is a skewed frequency distribution because of aberrant analytical data. Rejection of outlying results usually is required to obtain a better estimate of mean concentration values. The present work describes the application of an approach, based on skewness and kurtosis statistical rests, to establish reliable concentration values in study of rare-earth element compilations for GRM. Frequency histograms of initial concentrations for these elements differ significantly from a normal distribution, as deduced from their skewness a,ld kurtosis coefficients. The statistical procedure shows that rejection of outliers yields normal distributions which can be used to provide mean concentrations with smaller standard deviations for a large number of cases, although for many elements our %RSD are similar (within 5%) to literature values. This procedure has been applied to derive new concentration data for rare-earth elements in 26 GRM, which are compared with earlier compilations to show that the statistical procedure proposed here provides mean values with greater "quality value." Although most present mean concentrations are similar (within 5%) to those reported in previous literature, some of them are significantly different (with differences of up to 40%) in a few GRM.