The study was based on questionnaires sent to 10,000 companies, of which about a third replied.
So this week it sent questionnaires to 13,000 randomly selected Federal workers.
The video journal was begun with a questionnaire sent to a wide variety of interested people.
About 400 executives completed the poll in October, out of 6,000 who were sent questionnaires.
The questionnaire sent to the local council (the 'search') is inadequate.
In 1984 mothers were sent questionnaires four months after giving birth; 1508 of 1920 (79%) responded.
In 1989 mothers were sent questionnaires six months after giving birth; 1493 of 1977 (76%) responded.
This study sought to minimize a common problem with studies of its kind by repeatedly asking people who were sent questionnaires to return them.
The primary method of data collection was by sending questionnaires to subjects or their relatives.
The subcommittee staff sent questionnaires to 224 clinics nationwide and 190 of those responded.
