- Dr J Bourbeau, Respiratory Epidemiology Unit, McGill University, 1110 Pine Avenue West, Montreal, Quebec, Canada H3A 1A3.
- Received September 9, 1997
- Revision requested November 7, 1997
- Revised February 19, 1998
- Accepted February 27, 1998
- First published June 1, 1998.
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