1. A method comprising: prompting a first agent of a call center, by a data processing system associated with the first agent, while said first agent is serving a first call, for an estimate of how much longer said first agent will be serving said first call; receiving, by the data processing system, a first response from said first agent; storing, by the data processing system, one or more values based on said first response in a data store; prompting, by the data processing system, said first agent, while said first agent is serving a second call, for an estimate of how much longer said first agent will be serving said second call; receiving, by the data processing system, a second response from said first agent; storing, by the data processing system, one or more values based on said second response in said data store; computing a measure of how closely a plurality of service time estimates provided by said agent compare to actual remaining service times; and storing, by the data processing system, said measure in said data store.