The distinct differences in Group III compared to Groups I and II described above were further confirmed by examination of changes in individual transcripts for these groups ( Fig. 2A ). Group average p-value (GAP) criteria, based on a two-tailed z-test comparing z-scores for each drug abuse case to the four individually best-matched controls, was employed to identify individual transcripts for which expression was either increased or decreased in at least one of the groups identified by hierarchical clustering above.
