Methods of Tracing
Traceability means that costs can be assigned easily and
accurately, whereas
tracing
is the actual assignment of costs to a cost object using
an observable measure of the resources consumed by the cost object. Tracing costs
to cost objects can occur in one of two
ways: (1) direct tracing or (2) driver tracing.
Direct tracing
is the process of identifying and assigning costs that are exclusively
and physically associated with a cost object. This is most often accomplished by
physical observation.
Consider the pizza example. The cost object is Ryan Chesser’s
lunch. By observing that he has a small pizza, salad, and medium drink, we can
assign the cost of $6.50. The cost is directly traceable to him. As a second example,
let the cost object be a product: bicycles. The product uses both materials and labor.
It is easy to observe how many wheels, other parts, and hours of labor are required
to produce each bicycle. Both material and labor usages are physically observable,
and therefore, their costs can be directly charged to a bicycle. In both examples, the
cost objects are the
exclusive
consumers of the resources in ques
tion. Ideally, all costs
should be charged to cost objects using direct
tracing. Unfortu
nately, it is often the
case that cost objects are not the exclusive consumers of resources. In this case, we
appeal to driver tracing to assign costs.
Driver tracing
is the use of drivers to assign costs to cost objects. In a cost
assignment context,
drivers
are observable causal factors that
measure
a cost object’s
resource consumption. They are factors that cause changes in resource usage and
thus have a cause-and-effect relationship with the costs associated with a cost object.
For example, assume that Ryan Chesser and Shana Parker go to lunch together.
Shana and Ryan agree to share the cost of the lunch. They order a medium pizza
(divided into 10 slices) for $9, a pitcher of root beer for $2 (five glasses of content),
and Shana orders a small salad for $1. How much cost should be assigned to each
person? Note that the two share the pizza and root beer, whereas the salad is a
“resource” exclusive to Shana. The cost of the salad, then, is assigned by direct tracing ($1 to Shana and $0 to Ryan).
To assign the costs of the pizza and root beer,
drivers are chosen: slices of pizza and glasses of root beer, respectively. A rate is calculated per unit of resource (as measured by the drivers): $0.90 per slice of pizza
($9/10) and $0.40 per glass of root beer ($2/5). Next, usage of the driver is observed
for each person (cost object). Assume that Ryan eats seven slices of pizza and drinks
three glasses of root beer, with Shana consuming the remainder. Thus, the cost per
person is calculated as follows:
Shana Ryan
Salad (direct tracing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $1.00 $0.00
Pizza (driver tracing):
$0.90
3 slices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.70 —
$0.90
7 slices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . — 6.30
Root beer (driver tracing):
$0.40
2 glasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.80 —
$0.40
3 glasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . — 1.20
Totals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $4.50 $7.50
This simple pizza example of a shared resource extends into more complex busi-
ness settings. Inspecting products may be the “pizza” shared by precision surgical
instruments produced in a plant. The cost of inspection can be assigned to individ-
ual instruments (the cost objects) using number of inspection hours (“slices of
pizza”) consumed by each type of instrument. Consider, as a second example, the
cost of a heart monitor used by cardiac patients (the cost object). The heart monitor
is the “pizza,” and monitoring hours used could be the “slices of pizza” chosen to
assign the costs to cardiac patients. Thus, the tracing principles described by the
pizza example relate directly to costing within realistic business environments.
Driver tracing is usually less precise than direct tracing. However, if the cause-
and-effect relationship is sound, then a high degree of accuracy can be expected.
Consider, for example, the driver: number of slices of pizza. Suppose that the slices
are not exactly equal in size and that Shana chose to eat three of the smaller slices.
Thus, her cost for pizza is really less than $2.70. Even so, if the difference in the size
of slices is not great, then we can still say that the cost is accurate. Nonetheless, this
illustrates the importance of how we select, specify, and measure drivers. These more
detailed issues are explored in greater depth in Chapters 3 and 4. For now, it is sufficient to understand their role in cost assignment and that they can produce some-
what less accurate assignments than direct tracing. Of more immediate concern is
the situation where cost objects are not exclusive consumers of resources and where
no cause-and-effect relationship can be defined (or where using a causal relationship
is cost-prohibitive).