Cost Stickiness and Cost Inertia : A Two-Driver Model of Asymmetric Cost Behavior

In the asymmetric cost behavior model, managers play an active role in determining cost behavior by adding or removing resources as activity changes. Cost stickiness occurs when managers deliberately retain slack resources resulting from a decline in sales activity between periods. Because both sales and long-term capital investments change between periods, we estimate a model of cost behavior that includes two cost drivers: revenue as a volume of activity driver and property, plant and equipment (PP&E) as an assets-in-place driver. We associate cost inertia with slack resources retained when assets-in-place are reduced. We find that changes in SG&A costs separate between the two cost drivers, and that the explanatory power of an asymmetric cost behavior model including PP&E as a second driver is significantly greater than the explanatory power of the single-driver cost behavior model. Similar insights are obtained when we replace SG&A costs with employee headcount or employee costs as the cost measure of interest. In all cases, we find that the cost inertia term is significantly negative and relatively large in magnitude. We estimate an expanded model that conditions analysis of current year cost behavior on the direction of sales change in the previous period and find that the pattern of cost changes is consistent with both cost stickiness and cost inertia