Figure 2. Multi-component model of copy-number alteration.

(a) In a noisy system, a soft discriminator (red) is juxtaposed to a hard threshold (black); both of which assign points either continuous or binary values respectively (parentheses) for confidently copy-neutral or amplified loci (black) and for challenging cases at the margin of signal (green). This indicates the benefit of soft discrimination. (b) The functional form of the soft discriminator; a sigmoid function with parameters for location (E) and slope (β). (c) Individual-tumor approach to detecting gain and loss; the multi-component model parameterized for two tumors (red and blue) indicating that tumor-specific features produce different discriminators for single-copy gain and loss (solid), amplification (dot-dash), and homozygous deletion (dotted). Parameterization selects values for E and β such that their magnitude (unsigned) moves in the direction indicated (legend).