Predictive dialer algorithms "play the odds" in a manner similar to casinos.  Industry experience has shown that roughly 1 of every 3 dial attempts provides a live person with which your agent may talk, while the other attempts are unsuccessful with outcomes of busy, no answer, fax, unavailable number, etc.  The objective of predictive dialing is to maximize the probability of having exactly one live caller for each available agent, very shortly after the agent comes available.

To meet this objective, predictive dialers use a number of techniques, such as overdialing and pre-dialing.  When overdialing, a predictive dialer places multiple dial attempts for an available agent, so as to increase the odds of getting exactly one live caller. When pre-dialing, a predictive dialer begins dial attempts before the agent actually comes available, so as to decrease the wait time for the agent. As with the casinos, where the house doesn't always win, predictive dialers occasionally have more or less live callers than available agents.  Agents are also at times not available as quickly as anticipated when pre-dialing was initiated. When there are more live callers than available agents, dialers generally allow up to several seconds for an agent to come available, then disconnect the call.