The first study, by the Chinese University in 2001 and 2002, polled 327 female students aged 13 to 18 and found 47 per cent had thought about suicide. The second, by the same university of 371 boys and girls aged 14 to 20 in 2002 and 2003, found 52.6 per cent had done so.

The results were highlighted after police foiled an attempt by three teenage girls to kill themselves at Cheung Chau's Bela Vista resort on Sunday.

Psychology professor Catherine McBride-Chang, who led both studies, said that in the first one, study-related factors, including perceptions of academic performance and parents' dissatisfaction, as well as anxiety about tests, were cited as causes.

Test anxiety was also reported to be strongly related to depression. Students with a high degree of test anxiety were twice as likely to have thought about suicide.

Professor McBride-Chang said she knew of no previous studies that indicated such a 'robust relationship' between test anxiety and depression.

'There are reasons to think that the two are strongly correlated in Hong Kong and probably in other Asian countries, where the testing systems are fairly strict,' she said.

Professor McBride-Chang said the government should be aware of the link and provide support for students with a high degree of anxiety about tests to counteract the tendency towards depression.

In the second study, family-related factors, including family cohesion, family support and parent-adolescent conflict, were found to be related to depression and suicidal thoughts.

Significantly, more girls than boys had thought about suicide.

Professor McBride-Chang said some studies suggested more girls than boys would consider suicide at a lower level of depression.

She added that the figures were higher than those in North America, where a study among high school students found that about 25 per cent had thought of suicide.

Meanwhile, the Education and Manpower Bureau has sent psychologists to provide counselling to students at schools attended by the three girls who attempted suicide.

At one of them, the Salvation Army William Booth Secondary School, officials said the teenager's close friends were being counselled. The school, social workers and the bureau will closely monitor the girls and discuss arrangements for the student to return to school.

Response to the recent suicides of two teachers continued yesterday with a petition to Chief Executive Donald Tsang Yam-kuen urging a cut in teachers' workloads.

Handed in by the Education Employees General Union at the Central Government Offices, it called for standard working hours for teachers and a slowing of education reforms.

The union said it had interviewed 1,600 teachers from primary and secondary schools in September and October and more than 90 per cent said working hours should be set at eight hours a day.