Figure 1.

Selection of well measured cells. (a) Scatterplot of FACS data showing typical properties of morphologic parameters. FSC corresponds to cell size and SSC to cell granularity. Several subpopulations can be distinguished: (I) healthy and well measured cells, (II) cell debris, and (III) cell conjugates and air bubbles. (b) Robust fit of a bivariate normal distribution to the data. The ellipse represents a contour of equal probability density in the distribution and is used as a user-defined cut-off boundary (two standard deviations in this example). Points outside the ellipse (marked in red) are considered contaminants and are discarded from further analysis. Scatterplots of perturbation versus phenotype (c) before and (d) after removing contaminants. The proportion of outlier data points is reduced significantly. Here, they correspond to measurements with very small phenotype values (cell debris). FACS, fluorescence-activated cell sorting; FCS, forward light scatter; SSC, sideward light scatter.