Links between distributions, detection spectra and indicator functions. To illustrate important connections between gene score distributions, detection spectra, and indicator functions, we selected four categories from the imatinib data. (a) The category 'MAPKKK cascade' exhibits a heavy lower tail, exemplifying a low-proportion-high-effects enrichment of underexpressed genes. As expected, this category was detected by ZK and ZC. (b) The category 'EGF receptor signaling pathway' has normal tails but is left-shifted midway between the center and the tails, consistent with an intermediate-proportion-moderate-effects enrichment of underexpressed genes. This category was detected by AD. Whereas these two examples receive indicator values near -1 because they are enriched in underexpressed genes, category 'hematopoiesis' (c) exhibits a right-shifted distribution, implying indicator values near 1. (d) Category 'development', identified at a slightly higher false-discovery rate, has a heavy lower tail as well as a right-shifted center, and exemplifies mixed enrichments (intermediate AD, CM, ZA, and ZC indicator values).