제품과 활동사이의 소비구조가 복잡한 경우의 제품원가계산: 또 하나의 간과되어 온 ABC의 과제

초록

It has often been argued whether the introduction of an activity-based costing (ABC) system in an organization is desirable boils down to a cost/benefit analysis. The costs of introducing ABC systems here include those related with complexities of the mechanism of costing system as well as with the implementation of the system. Further, it has been a conventional wisdom, as argued by Cokins(2001), that product costing becomes more accurate as cost attribution procedure takes multi-stages when the traditional two-stage costing is inappropriate because of the lack of direct mapping between final cost objects and cost pools. However, this paper shows that using a usual bottom-up multi-stage costing procedure may not enhance the accuracy of product costing while it requires more cost. The purpose of this paper is to analyse a product costing problem in the presence of a multi-layered resource consumption structure, which has drawn little attention from among accounting academics but appears in most business situations. The usual two-stage procedure where resources are assigned to activities and then the costs of activities are assigned to products represents a typical ABC. This treatment requires direct mapping between activities and products clearly exist so that the amount of each activity consumed by each product can be easily measured. However, this is often not the case in practice as we can witness in many large organizations such as BT. The problem caused by the ubiquitous presence of indirect mapping was also well pointed out by Datar and Gupta(1994). But, there has been little serious attempts among academics to overcome it. To tackle this situation, accounting practitioners such as Cokins(2001) normally utilize the approach so called an “expanded ABC”. The importance of this problem in practice is exemplified by Cokins(2001) when he calls the invention of an expanded ABC one of the most important top 10 developments in the field of ABC since the late 1980s. He further argues that costing system has made a Darwinian evolution from the traditional volume-based costing to the simple (two-stage) ABC, which is argued to be “an obsolete two-stage ABC” in indirect mapping environments, and further to an expanded ABC, which is a kind of a bottom-up multi-stage costing model. However, this paper shows that an expanded ABC is not free from cost distortion after all. It provides an in-depth analysis of a multi-layered resource consumption structure and an expanded ABC, where costs of intermediate activities are attributed to the next higher level activity cost pools and thus these costs aggregated into the higher level activity cost pools are attributed to the next higher level cost pools together, using the single cost driver. The way costs are aggregated and attributed in expanded ABC causes cost distortion because the cost pool homogeneity and the proportionality of pool costs (the constancy of charge-out rates), which are essential for a costing system to provide accurate costs, are no longer maintained and violated in this procedure. Thus, contrary to the common belief, the expanded ABC can not generate an accurate product cost information. We show that an expanded ABC in effect assumes that all cost pools are unit-level cost pools with regard to the next higher level activities (and/or products). In order to provide an accurate product cost in multi-layered resource consumption environments, a multi-stage costing system must not aggregate the costs from lower level cost pools into the higher level cost pools, rather it must attribute each level of costs directly to final cost objects using a “top-down ABC,” approach, which we recommend to utilize. The suggested top-down ABC may be more costlier than a bottom-up expanded ABC or the usual two-stage ABC, the fact which renders the costing system designer the cost/benefit criterion.

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