Enrichment factors are often reported with respect to a random sample of the library for the top 100 compounds, EF random 100 , to reflect the typical size of an HTS screen. For NGT, EF random 100 = 733 (ASAH1) and EF random 100 = 1,402 (CDK5). NGT's generation of just under 1.2 million compounds for each target (Table ) to obtain a top 100 list was therefore equivalent to the explicit screening of more than 1.3 billion compounds from the 3 trillion space.