Chapter 6: variable costing and segment reporting: tools for management. Two general approaches are used for valuing inventories and cost of goods sold. One approach, called absorption costing, is generally used for external reporting purposes. The other approach, called variable costing, is preferred by some managers for internal decision making and must be used when an income statement is prepared in the contribution format. This chapter shows how these two methods differ from each other. It also explains how to create segmented contribution format income statements. Variable costing treats only those costs of production that vary with output as product costs. The cost of a unit of product consists of direct materials, direct labor, and variable overhead. Fixed manufacturing overhead, and both variable and fixed selling and administrative expenses are treated as period costs and deducted from revenue as incurred. Absorption costing treats all costs of production as product costs, regardless of whether they are variable or fixed.