article_snippet: In A study, 561 Rhode Island middle-school students were surveyed periodically over three years.
article_snippet: In most cases, they parents provided it – often at a party or other special occasion.
article_snippet: By the time 561 Rhode Island middle-school students reached the ages of 14 and 15,
article_snippet: Professor Mark Bellis, of Liverpool John Moores University, surveyed 16,000 people aged 14 to 17 in the North West of England.
article_snippet: More boys than girls had done so, and the rate increased among those from deprived areas, the journal BMC Public Health reports.