These problems have become obvious to most ABC implementers. But a subtle and more serious problem arises from the interview and survey process itself. When people estimate how much time they spend on a list of activities handed to them, they invariably report percentages that add up to 100. Few individuals report that a significant percentage of their time is idle or unused. Therefore, cost-driver rates are calculated assuming that resources are working at full capacity. But as we all know, operations often run at considerably less than their capacity. That means that the estimated cost-driver rates are usually much too high. (Technically, they will be overstated by the reciprocal of the capacity utilization percentage: At 80% utilization, the rates are 25% too high; at 67% utilization, the rates are 50% too high.)