This study aimed to determine whether : ( a ) higher vs. lower predictable money amounts ( $ 3 vs. $ 1 ; analogs of standard voucher-based CM ) increase cocaine demand elasticity ; and ( b ) probabilistic amounts matched for expected value with the $ 3-predictable amount ( 50 % chance of $ 6 ; 25 % chance of $ 12 ; and 12.5 % chance of $ 24 ; analogs of prize CM ) similarly affect cocaine choice .