Is concerned with the interaction of the experimental treatment with other factors and the resulting impact on the ability to generalize results to other times, settings, or persons.

Performance bicycle company makes steel and titanium handle bars for bicycles. it requires approximately 1 hour of labor to make one handle bar of either type. during the most recent accounting period, barr company made 7,700 steel bars and 2,300 titanium bars. setup costs amounted to $35,000. one batch of each type of bar was run each month. if a single company-wide overhead rate based on direct labor hours is used to allocate overhead costs to the two products, the amount of setup cost assigned to the steel bars will be: