RT Journal Article SR Electronic T1 Measuring sexual behaviour: methodological challenges in survey research JF Sexually Transmitted Infections JO Sex Transm Infect FD BMJ Publishing Group Ltd SP 84 OP 92 DO 10.1136/sti.77.2.84 VO 77 IS 2 A1 Kevin A Fenton A1 Anne M Johnson A1 Sally McManus A1 Bob Erens YR 2001 UL http://sti.bmj.com/content/77/2/84.abstract AB