A telephone company's district office has received no complaint of calls being cut off from subscribers in the hill tehsil, and its report concludes that the network serves that tehsil well. An answer to which of the following questions would be of most use in judging the report's conclusion?

The report turns silence into a good report, and silence is worth something only where a dissatisfied subscriber had an open and known way of breaking it. If the only way of complaining is a call on the network that keeps failing, the tehsil's silence is exactly what a bad network would produce, and the report's evidence works out to nothing. The tariff bears on what the service costs; the age of the tower and the number of towers in the district describe the plant, and none of the three tells us whether a complaint from that tehsil could have reached the office at all.