where B is the variable of interest (i.e., either smoking quantity or nicotine dependence score), A is the set of all other variables (i.e., gender and depending on what B is at the moment, nicotine dependence score or smoking quantity), RAB2 is the proportion of variance accounted for by A and B together (relative to a model with no regressors), and RA2 is the proportion of variance accounted for by A (relative to a model with no regressors). Thus, the numerator of (2) reflects the proportion of variance uniquely accounted for by B, over and above that of all other variables (Cohen, 1988).
