Scatter of l-skewness versus l-kurtosis of gene expressions for the four data sets - "Craniofacial", "Liver", "Brain" and "Housekeeping". The scatter is overlaid on the relationships between these moments for standard theoretical distributions. The legend for these distributions is provided in Figure 5. The l-skewness and l-kurtosis for the unaffected probe sets with mean expression greater than 6 for the "Craniofacial", "Liver", "Brain" and "Housekeeping" datasets are plotted in the subplots (a), (b), (c) and (d) respectively. The intensity of red of each circle that represents a probe set in these subplots is made to vary linearly with the mean expression of this probe set. So higher the mean expression, the greater is the intensity of red.