Data summary by cohort and country.

*Cohort size = Number of enrolled participants eligible for this study (see text for details regarding the inclusion criteria). Participants at follow up (%) = number of participants at follow-up divided by cohort size (x100).1Data referred to the percentage of Internet users in 2011 and were gathered from the International Telecommunication Union (ITU, www.itu.int), the United Nations specialized agency for information and communication technologies.Data summary by cohort and country.