A district office must decide whether to keep running a small ferry between two villages on opposite banks of a river, at a cost it finds heavy. An answer to which of the following questions would be of most use in reaching that decision?

The office already knows what the ferry costs; what it does not know is what would be lost by stopping it. If a bridge stands a short walk upstream the loss is small, whereas a half-day journey round would make the ferry worth its cost. The year it began and the length of a crossing are description rather than decision, and the number of staff is part of the cost the office has already weighed.