When used to determine the concentrations of chemical elements in samples, X-ray intensity measurements are processed by correction programmes. These measurements are now usually obtained with fully or partially automated instruments. In order to suppress useless computations on sets of results containing rogue values, statistical tests must first be applied to the original experimental data. From an economic standpoint, it may also be worthwhile to reject the outlying counts automatically rather than discard complete sets of measurements. Statistical tests permitting the detection of outliers in groups of results are described.