Students' responses were compiled from the 2007 Philadelphia Youth Behavioural Risk Survey (YRBS). Respondents were asked how many cigarettes they had per day over 30 days, and how many days over a 30-day period they had five or more drinks in a row.

'Those numbers resulted in very few studies which looked at both smoking and binge drinking in a diverse sample, most focused only on instances of these in Caucasian or Hispanic adolescents,' said Daly.