BRD2 and acute lymphoblastic leukemia: To measure the level of attribution it is common to express the fraction of attributable risk10 (fraction of attributable risk (FAR) = 1 − PNAT/PALL) or simply the risk ratio (RR = PALL/PNAT), where PNAT and PALL denote the probability to exceed the observed event magnitude in the NAT and ALL ensembles, respectively.