Fifth, time series data support only a weak form of causal inference (Granger causality54,55), where earlier events may cause later events but not vice versa (e.g., the observed decrease in NF-κB binding was followed by a downregulation of B cell transcription factors and an erosion of B cell identity among the CLL cells). This evidence concerns the gene NFKB1 and B-cell chronic lymphocytic leukemia.