DEA best practices: raw vs. normalized data
Hi all,
I am searching for best practices in DEA using scanpy.
I can't find it back but I remember reading somewhere that DEA should be done on raw expression data rather than normalized data. However in scanpy tutorials they seem to perform it on log normalized data. Moreover, scanpy.tl.rank_genes_groups throws a Warning if it does not recognize log transformed data (which I think is because the Fold Change is computed using an exponential to reverse the log, so if it has raw data it applies an exp to it which is not logical).
Thank you for any precious insight,
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Depends on the test. If you use tests that use data "as-is", for example t-test, Wilcoxon, limma-trend, etc, then normalization must be done before. In almost all cases you want to log-transform. Other tests such as edgeR use the normalization as part of their model with offsets.