How do committed fixed costs differ from discretionary fixed costs? OA Discretionary fixed costs usually must be incurred for some time, and thus a great effort is needed to change or eliminate them, OB, Discretionary fixed costs are flexible and could be increased or eliminated entirely on short notice if necessary, where Oc. Discretionary fixed costs are not immediately affected by changes in the cost-driver level, where committed fixed change in OD. Discretionary fixed costs change in direct proportion to the cost-driver level, where committed fixed costs are not immediately where committed fixed costs are flexible and could be increased or eliminated entirely on short notice if necessary. committed fixed costs usually must be incurred for some time, and thus greater effort is needed to change or eliminate them. direct proportion to the cost-driver level. affected by changes in the cost-driver level