Mediation model for the association between pre-treatment cocaine use (X, in the 28 days prior to treatment), hippocampus volume at treatment onset (M, measured as the average volume of the left and right hippocampus), and treatment outcome (Y, calculated as percentage of cocaine-negative urine samples during treatment ā where higher percentage represents better outcome). Path coefficients are shown next to arrows indicating each link in the analysis, with standard errors in parentheses. Path a refers to the path from X to M. Path b refers to the direct link between M and Y. Paths c and cā refer to the association between X and Y, with and without the mediator M, respectively.* p<.05, ** p<.01, *** p<.001.