Traditional methods of allocating manufacturing overhead
Let's look at several methods used to allocate manufacturing overhead. Keep in mind that if the method does not allocate the true amount of factory overhead, the cost per unit of product will be wrong and could result in management making a flawed decision. As you review these method, ask yourself for each given product, will the allocated amount of overhead reflect the actual amount of overhead used in that item's production? If a cause-and-effect relationship is not evident, is there at least an obvious correlation between manufacturing overhead and the basis for the allocation (such as machine hours)? If there is no correlation, the allocation method is suspect and could result in the improper amount of overhead being assigned to individual products.
Allocating manufacturing overhead via direct labor
In the early 1900s it was logical to allocate manufacturing overhead on the basis of direct labor hours (or direct labor cost). The manufacturing process was not automated, there were hardly any variations in the products made (think Model T cars), and customers did not demand such things as just-in-time deliveries or bar coding. In those day, when manufacturers increased the amount of direct labor, there was likely to be a related increase in such things as the number of factory supervisors, the factory space to be maintained, and factory supplies and utilities consumed. In other words, there was a high degree of correlation between the quantity of direct labor used and the amount of manufacturing overhead used. By allocating manufacturing overhead on the basis of direct labor hours, a product requiring 30 direct labor hours would be allocated twice as much manufacturing overhead as a product requiring 15 direct labor hours.