aExponent Health Sciences Group, Exponent, Inc., Washington, District of Columbia
bDepartment of Epidemiology, Harvard School of Public Health, Boston, Massachusetts
cExponent Health Sciences Group, Exponent, Inc., Alexandria, Virginia
dDepartment of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA
eDepartment of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden
Correspondence to Dr Pamela J. Mink, PhD, MPH, Exponent, Inc., 1730 Rhode Island Ave., NW, Suite 1100, Washington, DC 20036, USA
Tel: +1 202 772 4921; fax: +1 202 772 4979; e-mail: [email protected]
Received 20 September 2006 Accepted 21 September 2006