London: Thirty-six percent of teens, especially 15-year-old boys and girls, don't tell parents where they were at night, even though they might be into in risky behaviour such as smoking or drinking, a study reveals.

The finding is based on a long-term study of 40,000 British households, which asked more than 2,000 teenagers aged 10 to 15 years how frequently they stayed out past 9.00 p.m., without telling their parents.

Researcher Maria Iacovou, from the Institute for Social and Economic Research, University of Essex, who analysed the data, said: "Staying out late does not cause young people to smoke and drink, but regularly staying out late without telling their parents where they are is symptomatic of a young person with underlying problems."

The study, funded by the Economic and Social Research Council (ESRC), also found that staying out late, without telling your parents, may be affected by the quality of the emotional relationship the child has with their parents, according to an university statement.

Regularly staying out late is linked with visiting pubs or bars more often; with frequency of alcohol consumption; with smoking, and with cannabis use.

Sixty-four percent of 15-year-old girls who stay out frequently past 9 p.m., without their parent's knowledge, consumed alcohol more than once in the last month, compared with only 25 percent of girls who hadn't stayed out in the past month.

Eighteen percent of the teenage girls who have not stayed out past 9 p.m. smoked. This rises to 51 percent among girls who stay out frequently.

Five times more boys who frequently stay out late, report ever having used cannabis, compared to boys who do not stay out late.