Data collection procedure
Data collection was carried out from March to May 2001 in the United States (Chicago and Boston), October 2002 in Australia (Melbourne), and July 2002 in Britain (Glasgow). Procedures were standardised at the three sites (except where noted). Each youth attended a rating session with 15 other youth in which they appraised 10 different adverts in a 75 minute period. Groups were facilitated by study personnel, who explained the purpose and format of the session and empha- sised the importance of each participant providing honest evaluation of the adverts. Each advert was shown twice, after which the participants completed a one page rating form per advert.