Another problem is that ABC uses a single driver rate
for each activity. Hence, it is difficult to model multi-driver
activities. For example, patient registering costs at an outpatient
clinic not only depend upon the number of patients
registered, but also on the type of patient (known versus
unknown). Working with an average cost per patient
of D 5 thereby provides inaccurate cost information. One
could suggest splitting the activity into two activities, such
as “registration of known patients” and “registration of
unknown patients.” However, splitting inflates the number
of activities in ABC and creates difficulties in estimating the
practical capacity for each sub-activity.1
The solution to the problems with ABC is not to abandon
the concept. Instead, Kaplan and Anderson [14,16] developed
a new approach to ABC, called time-driven ABC. The
new procedure starts, as with the traditional ABC approach,
by estimating the cost of supplying capacity. The TDABC
approach identifies the different departments, their costs
and their practical capacity. For healthcare operations, the
practical capacity is expressed as the amount of time that
employees can work, without idle time. Often practical
capacity is estimated as a percentage, say 80% or 85%, of
theoretical capacity [14–18,20]. By dividing the total cost by
the practical capacity, the cost per time unit is calculated.
Costs then are assigned to the cost object by multiplying
the cost per time unit by the time needed to perform the
activity, as shown in Panel B of Table 1.
The breakthrough of TDABC lies in the time estimation
[18]. The time-driven ABC procedure uses an estimate
of the time required each time the activity is performed.
It is important to stress, though, that the question is not
about the percentage of time an employee spends doing
an activity (e.g., registering patients) but how long it takes
to complete one unit of that activity (the time required
to register one patient). In addition, not all patients are
the same and require the same amount of time to register.
Rather than define a separate activity for every
possible combination of patient characteristics (known
or unknown), or use a duration driver for every possible
patient registration combination, the time-driven
approach estimates the resource demand by a simple
time equation. These time equations model how different
time drivers (i.e. case-specific characteristics) drive the
time spent on activity. In complex environments where
the time needed to perform an activity is driven by
many drivers, TDABC can include multiple drivers for each
activity. As such, time equations greatly simplify the estimating
process and produce a far more accurate cost
model than would be possible using traditional ABC techniques.