We found a matchYour institution may have access to this item. Find your institution then sign in to continue.TitleThree authors reply.AuthorsEl-Sayed AM; Scarborough P; Galea SPublicationAmerican journal of epidemiology, 2013, Vol 178, Issue 5, p838ISSN1476-6256Publication typearticleDOI10.1093/aje/kwt184