What are you basing performance on? What type of call center? If you are a telemarketing company you cannot blame the agent if he get’s hang ups or no answers. Personally I don’t answer my phone unless I have a valid caller ID. If this is a customer support call center, some problems may take longer to resolve and this would mean the agent has lower call volume.. More details on the type of call center, agent’s duties and reason to look at their performance are needed to give a more specific answer.