Time Horizon
Whether a cost is variable or fixed with respect to a particular activity depends on the
time horizon being considered in the decision situation. The longer the time horizon, all
other things being equal, the more likely that the cost will be variable. For example,
inspection costs at Boeing Company are typically fixed in the short run with respect to
inspection-hours used because inspectors earn a fixed salary in a given year regardless of
the number of inspection-hours of work done. But, in the long run, Boeing’s total inspection
costs will vary with the inspection-hours required: More inspectors will be hired if
more inspection-hours are needed, and some inspectors will be reassigned to other tasks
or laid off if fewer inspection-hours are needed.