To resolve the cluster of appliance failures, an appliance-service analyst treats these possibilities as exhaustive: a defective manufacturing batch, improper installation, voltage problems, or user misuse. Improper installation can be rejected because certified installers handled the failed units; voltage problems can be rejected because homes with failures had normal voltage readings; and user misuse can be rejected because the failures occurred before ordinary use began. From this, an appliance-service analyst concludes that the remaining explanation is a defective manufacturing batch. Which choice best describes the method used?