Epidemiology and Social: Original Papers
Moore, Richard D.; Chaisson, Richard E.
From the Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Sponsorship: Supported by the National Institute on Drug Abuse (RO1-DA-11602), the Agency for Health Care Policy and Research (RO1-HS-07809), and the Food and Drug Administration (FD-U-000977).
Correspondence to Richard D. Moore, MD, Johns Hopkins University School of Medicine, 1830 E., Monument Street, _Room 8059, Baltimore, MD 21205, USA._Tel: +1 410 955 2144; fax: +1 410 955 4634.
Received: 13 April 1999; revised: 16 June 1999; accepted: 24 June 1999.