Rscreenorm: normalization of CRISPR and siRNA screen data for more reproducible hit selection

Costa Bachas, Jasmina Hodzic, Johannes C. van der Mijn, Chantal Stoepker, Henk M. W. Verheul, Rob M. F. Wolthuis, Emanuela Felley-Bosco, Wessel N. van Wieringen, Victor W. van Beusechem, Ruud H. Brakenhoff, Renée X. de Menezes

Reproducibility of hits from independent CRISPR or siRNA screens is poor. This is partly due to data normalization primarily addressing technical variability within independent screens, and not the technical differences between them. We present "rscreenorm", a method that standardizes the functional data ranges between screens using assay controls, and subsequently performs a piecewise-linear normalization to make data distributions across all screens comparable. In simulation studies, rscreenorm reduces false positives. Using two multiple-cell lines siRNA screens, rscreenorm increased reproducibility between 27 and 62% for hits, and up to 5-fold for non-hits. Using publicly available CRISPR-Cas screen data, application of commonly used median centering yields merely 34% of overlapping hits, in contrast with rscreenorm yielding 84% of overlapping hits. Furthermore, rscreenorm yielded at most 8% discordant results, whilst median-centering yielded as much as 55%. Rscreenorm yields more consistent results and keeps false positive rates under control, improving reproducibility of genetic screens data analysis from multiple cell lines.