Submitted on: 30 November 1998.
Revised on: 06 January 1999.
Accepted on: 18 January 1999.
PREVENTION SCIENCE---SPRINGER/PLENUM PUBLISHERS
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Submitted on: 12 May 1998.
Revised on: 18 June 1998.
Accepted on: 06 July 1998.
PREVENTION SCIENCE
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