Why are some cell lines not showing up in the results when certain genes are searched in the combined RNAi dataset?

Differences in the shRNA libraries used to screen different cell lines can lead to differences in the set of gene scores being available. Most notably, cell lines screened using only the Novartis DRIVE libraries will only have gene scores for around half of genes. Additional constraints on the set of shRNAs targeting a given gene can also influence whether gene scores will be available for a given gene. See the DEMETER2 paper for more details.