Group dialing has the same basic sample management requirements as Extension dialing. The same properties in DPM are used for dialer, dial, and call result configuration. Likewise, the same underlying sample management provider is used to get sample records to dial. The only real difference is that interviewers are associated with a group and calls are then made for the group instead of for the extension. When a group call is connected it is transferred to the interviewer who has been waiting the longest in that group.

For extension dialing, interviewer wait times can vary greatly between attempts to connect a respondent, as one request might get several no answers, while another obtains a connection first time. However, for group dialing, the wait time is effectively the average time taken to get a connected call for the group of waiting interviewers. In other words, the wait time variation should be smaller for group dialing than for extension dialing because the first connected call is given to the interviewer who has been waiting the longest.

Besides averaging out the wait time, group dialing can also reduce waiting times by predictively dialing more calls than there are waiting interviewers. Predictive dialing algorithms attempt to strike a balance between maximizing productivity (by reducing waiting times) and minimizing silent calls caused when a call is connected and there is no interviewer available to take the call.

Preview dialing is handled differently when dialing for a group of interviewers. When an interviewer requests a record, the sample management system locates the first eligible record for that interviewer and tests whether this record needs previewing. If the first eligible record needs previewing, sample management returns the record to the interviewer without dialing the number. The interviewer has time to preview the record and read the comments before returning the record either to the dialer for dialing or back to sample management. If the first eligible record does not need previewing, sample management sets the extension available for group dialing and increments the count of waiting interviewers. The record is then dialed for the group. Note that the record is unlikely to be returned to the original interviewer as it will be connected to the interviewer who has been waiting the longest.

All interviewers in a group should use the same interviewing engine whenever possible. If the engine load balancing script finds that an engine is very overloaded, it will allocate new interviews to a different interviewing engine in order to balance load. However, splitting the group in this way makes predictive dialing less efficient.

There is a separate dialing group for each combination of interviewer qualifications. Although this means there are more groups, it reduces the number of interviewers in each group which greatly simplifies the routing of calls to waiting interviewers.

Each unique set of qualifications is assigned a number which is appended to the project name to form the group name; for example, PROJ1:1.

The interviewer session engine maps interviewer qualifications to group ID numbers. New interviewer qualification groups are created as necessary when interviewers log in. The ID is passed to the dialing provider via the InterviewerQualGroup interview property.

Hook status is monitored by subscribing to the OnInfoChanged event from the extension object for each waiting interviewer.

See OnInfoChanged.

If the extension for a waiting interviewer goes on hook, the interviewer is removed from the table of waiting interviewers and an error is returned to the interviewer. Because the number of waiting interviewers is based on the number of entries in the table of waiting interviewers, the detection of an extension going on-hook is immediately reflected in the predictive dialing algorithm.

Fail-over occurs in the same way as it does for extension dialing.

Various dialing statistics are available from the Dialing Statistics object that exists for each dialing group. These include:

The object also provides a number of helper methods that can be used to provide summaries of the data for call attempts and active calls.