This measure asks adolescents how many vehicles and computers their family owns, whether they have a bedroom to themselves

and how many holidays they have had with their family in the past year. Items were summed to give an overall family affluence score (range 0–10), which was split into tertiles: ‘low’ (scores of 0–4), ‘medium’ (scores of 5–6) and ‘high’ (scores of 7–10). Participants were asked whether they smoked (yes/no). Sexual experience was assessed by asking participants ‘Have you ever had vaginal sex?’ (yes/no); this question was adapted from the ‘National Survey Caspase activation of Sexual Attitudes and Lifestyles’ [17]. Expectation of having sex in the next year was also assessed using two items adapted from Sheeran and Orbell [36]: ‘I expect I will have sex this year’ and ‘I think I will have sex this year’ (5-point scale: ‘strongly disagree’ to ‘strongly agree’, scored from 1 to 5). These items correlated highly (r = 0.97) and were summed to give an overall score which was split into tertiles: ‘no expectation’ (scores of 2), ‘low expectation’ find more (3–5) and ‘high expectation’ (6–10)

of having sex in the next year. Intention to attend cervical screening in the future was assessed using similar items: ‘When I am older and am invited to go for a smear (Pap) test, I intend to go’ and ‘When I am older and am invited to go for a smear (Pap) test, I will try to go’ (with a 5-point response scale as before). The items correlated highly (r = 0.89) and were summed to give an overall screening intention score which was split into secondly tertiles: ‘low intention’ (scores of 2–6), ‘medium intention’ (7–8) and ‘high intention’ (9–10). Other measures in the questionnaire that are not reported here have been described elsewhere [34]. After reading a brief description of the HPV vaccine (see Box 1) participants were asked to indicate their vaccine status (response options: ‘I have had all 3 doses of the HPV vaccine’; ‘I have had 1 or 2 doses of the HPV vaccine’; ‘I have been offered the HPV vaccine but I haven’t had it’; ‘I have not been offered the HPV vaccine’;

‘I don’t know’). Human papillomavirus (HPV) is a very common infection involved in most cervical cancer. It is transmitted via skin-to-skin contact, most commonly during sexual activity. A vaccine was developed that protects against this infection. You should have been offered the HPV (cervical cancer) vaccine in Year 8. It involved having three injections over about 6 months. Logistic regression analyses, clustering by school and cohort, were used to examine the association between HPV vaccine status (fully vaccinated versus un-/under-vaccinated) and other risk factors for cervical cancer. It is necessary to adjust for clustering of data within schools and cohorts in order to obtain unbiased tests of significance. Analyses were performed using the Complex Samples function in SPSS v.20 [37].